diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/queries/micro_external_sort/micro_external_sort.sqlpp b/asterixdb/asterix-app/src/test/resources/optimizerts/queries/micro_external_sort/micro_external_sort.sqlpp
new file mode 100644
index 0000000..a075cd1
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/queries/micro_external_sort/micro_external_sort.sqlpp
@@ -0,0 +1,52 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+// testing micro external sort in a subplan
+drop dataverse test if exists;
+create dataverse test;
+use test;
+
+set `compiler.sortmemory` "130KB";
+
+with ds AS (
+from range(0,89999) i
+select value {"id": i, "a":
+CASE ( i % 3)
+WHEN 0 THEN "one"
+WHEN 1 THEN "two"
+WHEN 2 THEN "three"
+END,
+"b": CASE ( (i div 3) % 3)
+WHEN 0 THEN "SUM_1s"
+WHEN 1 THEN "SUM_2s"
+WHEN 2 THEN "SUM_3s" END,
+"c": CASE ((i div 3) % 3)
+WHEN 0 THEN 1
+WHEN 1 THEN 2
+WHEN 2 THEN 3 END})
+SELECT `group`,
+(SELECT group_num, sum(g.d.c) AS sum
+FROM g
+GROUP BY g.d.b AS group_num
+ORDER BY sum
+) AS sum_per_group
+FROM ds d
+GROUP BY d.a AS `group`
+GROUP AS g
+ORDER BY `group`;
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/ASTERIXDB-2402.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/ASTERIXDB-2402.plan
index 2918193..f3dbc01 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/ASTERIXDB-2402.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/ASTERIXDB-2402.plan
@@ -10,7 +10,7 @@
                               -- AGGREGATE  |LOCAL|
                                 -- NESTED_TUPLE_SOURCE  |LOCAL|
                             }
-                      -- IN_MEMORY_STABLE_SORT [$$200(ASC)]  |LOCAL|
+                      -- MICRO_STABLE_SORT [$$200(ASC)]  |LOCAL|
                         -- ASSIGN  |LOCAL|
                           -- UNNEST  |LOCAL|
                             -- SUBPLAN  |LOCAL|
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.10.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.10.plan
index 6b66a53..f9d98dd 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.10.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.10.plan
@@ -7,7 +7,7 @@
                   {
                     -- AGGREGATE  |LOCAL|
                       -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$62(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$62(ASC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
             -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.11.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.11.plan
index dd3bb8f..55e2f55 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.11.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.11.plan
@@ -7,13 +7,13 @@
                   {
                     -- AGGREGATE  |LOCAL|
                       -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$62(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$62(ASC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
                   {
                     -- AGGREGATE  |LOCAL|
                       -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$67(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$67(ASC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
             -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.12.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.12.plan
index 1766fc3..469fa47 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.12.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.12.plan
@@ -11,7 +11,7 @@
                   {
                     -- AGGREGATE  |LOCAL|
                       -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$66(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$66(ASC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
             -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.13.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.13.plan
index 98c4c4f..d89ba4a 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.13.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.13.plan
@@ -7,7 +7,7 @@
                   {
                     -- AGGREGATE  |LOCAL|
                       -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$76(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$76(ASC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
                   {
@@ -17,7 +17,7 @@
                   {
                     -- AGGREGATE  |LOCAL|
                       -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$86(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$86(ASC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
             -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.14.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.14.plan
index b563fef..aa3554b 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.14.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.14.plan
@@ -7,7 +7,7 @@
                   {
                     -- AGGREGATE  |LOCAL|
                       -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$100(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$100(ASC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
                   {
@@ -17,13 +17,13 @@
                   {
                     -- AGGREGATE  |LOCAL|
                       -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$110(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$110(ASC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
                   {
                     -- AGGREGATE  |LOCAL|
                       -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$105(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$105(ASC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
             -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.16.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.16.plan
index ab82bf0..79505b4 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.16.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.16.plan
@@ -7,7 +7,7 @@
                   {
                     -- AGGREGATE  |LOCAL|
                       -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$x(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$x(ASC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
                   {
@@ -18,13 +18,13 @@
                   {
                     -- AGGREGATE  |LOCAL|
                       -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$z(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$z(ASC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
                   {
                     -- AGGREGATE  |LOCAL|
                       -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$y(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$y(ASC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
             -- ONE_TO_ONE_EXCHANGE  |LOCAL|
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.17.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.17.plan
index 6249d46..61ecb60 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.17.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.17.plan
@@ -10,13 +10,13 @@
                         {
                           -- AGGREGATE  |LOCAL|
                             -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                              -- IN_MEMORY_STABLE_SORT [$$106(ASC)]  |LOCAL|
+                              -- MICRO_STABLE_SORT [$$106(ASC)]  |LOCAL|
                                 -- NESTED_TUPLE_SOURCE  |LOCAL|
                         }
                         {
                           -- AGGREGATE  |LOCAL|
                             -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                              -- IN_MEMORY_STABLE_SORT [$$111(ASC)]  |LOCAL|
+                              -- MICRO_STABLE_SORT [$$111(ASC)]  |LOCAL|
                                 -- NESTED_TUPLE_SOURCE  |LOCAL|
                         }
                   -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
@@ -58,13 +58,13 @@
                         {
                           -- AGGREGATE  |LOCAL|
                             -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                              -- IN_MEMORY_STABLE_SORT [$$124(ASC)]  |LOCAL|
+                              -- MICRO_STABLE_SORT [$$124(ASC)]  |LOCAL|
                                 -- NESTED_TUPLE_SOURCE  |LOCAL|
                         }
                         {
                           -- AGGREGATE  |LOCAL|
                             -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                              -- IN_MEMORY_STABLE_SORT [$$129(ASC)]  |LOCAL|
+                              -- MICRO_STABLE_SORT [$$129(ASC)]  |LOCAL|
                                 -- NESTED_TUPLE_SOURCE  |LOCAL|
                         }
                   -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.9.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.9.plan
index 6d8202e..4199770 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.9.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/aggregate-sql-sugar/distinct_mixed/distinct_mixed.9.plan
@@ -7,7 +7,7 @@
                   {
                     -- AGGREGATE  |LOCAL|
                       -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$58(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$58(ASC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
             -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/group-by/sugar-06-distinct.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/group-by/sugar-06-distinct.plan
index f4eea8a..aeeb046 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/group-by/sugar-06-distinct.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/group-by/sugar-06-distinct.plan
@@ -12,7 +12,7 @@
                             {
                               -- AGGREGATE  |LOCAL|
                                 -- MICRO_PRE_SORTED_DISTINCT_BY  |LOCAL|
-                                  -- IN_MEMORY_STABLE_SORT [$$45(ASC)]  |LOCAL|
+                                  -- MICRO_STABLE_SORT [$$45(ASC)]  |LOCAL|
                                     -- NESTED_TUPLE_SOURCE  |LOCAL|
                             }
                       -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/insert-return-custom-result.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/insert-return-custom-result.plan
index ef733cb..b85e9b0 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/insert-return-custom-result.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/insert-return-custom-result.plan
@@ -5,7 +5,7 @@
               {
                 -- ASSIGN  |LOCAL|
                   -- ASSIGN  |LOCAL|
-                    -- IN_MEMORY_STABLE_SORT [$$16(ASC)]  |LOCAL|
+                    -- MICRO_STABLE_SORT [$$16(ASC)]  |LOCAL|
                       -- NESTED_TUPLE_SOURCE  |LOCAL|
               }
         -- COMMIT  |PARTITIONED|
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/micro_external_sort/micro_external_sort.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/micro_external_sort/micro_external_sort.plan
new file mode 100644
index 0000000..4f8ff43
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/micro_external_sort/micro_external_sort.plan
@@ -0,0 +1,27 @@
+-- DISTRIBUTE_RESULT  |LOCAL|
+  -- ONE_TO_ONE_EXCHANGE  |LOCAL|
+    -- STREAM_PROJECT  |LOCAL|
+      -- ASSIGN  |LOCAL|
+        -- ONE_TO_ONE_EXCHANGE  |LOCAL|
+          -- PRE_CLUSTERED_GROUP_BY[$$145]  |LOCAL|
+                  {
+                    -- AGGREGATE  |LOCAL|
+                      -- MICRO_STABLE_SORT [$$149(ASC)]  |LOCAL|
+                        -- MICRO_PRE_CLUSTERED_GROUP_BY[$$146]  |LOCAL|
+                                {
+                                  -- AGGREGATE  |LOCAL|
+                                    -- AGGREGATE  |LOCAL|
+                                      -- NESTED_TUPLE_SOURCE  |LOCAL|
+                                }
+                          -- MICRO_STABLE_SORT [$$146(ASC)]  |LOCAL|
+                            -- ASSIGN  |LOCAL|
+                              -- NESTED_TUPLE_SOURCE  |LOCAL|
+                  }
+            -- ONE_TO_ONE_EXCHANGE  |LOCAL|
+              -- STABLE_SORT [$$145(ASC)]  |LOCAL|
+                -- ONE_TO_ONE_EXCHANGE  |UNPARTITIONED|
+                  -- STREAM_PROJECT  |UNPARTITIONED|
+                    -- ASSIGN  |UNPARTITIONED|
+                      -- ASSIGN  |UNPARTITIONED|
+                        -- UNNEST  |UNPARTITIONED|
+                          -- EMPTY_TUPLE_SOURCE  |UNPARTITIONED|
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/nest_aggregate.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/nest_aggregate.plan
index d4cdff4..0b8a56d 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/nest_aggregate.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/nest_aggregate.plan
@@ -8,13 +8,13 @@
                     {
                       -- AGGREGATE  |LOCAL|
                         -- STREAM_LIMIT  |LOCAL|
-                          -- IN_MEMORY_STABLE_SORT [$$39(ASC)]  |LOCAL|
+                          -- MICRO_STABLE_SORT [$$39(ASC)]  |LOCAL|
                             -- MICRO_PRE_CLUSTERED_GROUP_BY[$$51]  |LOCAL|
                                     {
                                       -- AGGREGATE  |LOCAL|
                                         -- NESTED_TUPLE_SOURCE  |LOCAL|
                                     }
-                              -- IN_MEMORY_STABLE_SORT [$$51(ASC)]  |LOCAL|
+                              -- MICRO_STABLE_SORT [$$51(ASC)]  |LOCAL|
                                 -- STREAM_SELECT  |LOCAL|
                                   -- NESTED_TUPLE_SOURCE  |LOCAL|
                     }
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/nested_loj3.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/nested_loj3.plan
index 957a2ee..9232477 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/nested_loj3.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/nested_loj3.plan
@@ -19,7 +19,7 @@
                                       -- STREAM_SELECT  |LOCAL|
                                         -- NESTED_TUPLE_SOURCE  |LOCAL|
                                 }
-                          -- IN_MEMORY_STABLE_SORT [$$31(ASC), $$32(ASC), $$33(ASC)]  |LOCAL|
+                          -- MICRO_STABLE_SORT [$$31(ASC), $$32(ASC), $$33(ASC)]  |LOCAL|
                             -- STREAM_SELECT  |LOCAL|
                               -- NESTED_TUPLE_SOURCE  |LOCAL|
                     }
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/query-ASTERIXDB-1263.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/query-ASTERIXDB-1263.plan
index f2adbf6..241257b 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/query-ASTERIXDB-1263.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/query-ASTERIXDB-1263.plan
@@ -15,7 +15,7 @@
                                 -- AGGREGATE  |LOCAL|
                                   -- NESTED_TUPLE_SOURCE  |LOCAL|
                               }
-                        -- IN_MEMORY_STABLE_SORT [$$19(ASC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$19(ASC)]  |LOCAL|
                           -- ASSIGN  |LOCAL|
                             -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/query-issue785.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/query-issue785.plan
index 4405b9d..612a9b7 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/query-issue785.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/query-issue785.plan
@@ -7,7 +7,7 @@
                   {
                     -- AGGREGATE  |LOCAL|
                       -- STREAM_LIMIT  |LOCAL|
-                        -- IN_MEMORY_STABLE_SORT [$$62(DESC)]  |LOCAL|
+                        -- MICRO_STABLE_SORT [$$62(DESC)]  |LOCAL|
                           -- NESTED_TUPLE_SOURCE  |LOCAL|
                   }
             -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/similarity/jaccard-similarity-join-dual-order.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/similarity/jaccard-similarity-join-dual-order.plan
index e8b029a..e7ac5d6 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/similarity/jaccard-similarity-join-dual-order.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/similarity/jaccard-similarity-join-dual-order.plan
@@ -23,7 +23,7 @@
                                     -- PRE_CLUSTERED_GROUP_BY[$$126]  |PARTITIONED|
                                             {
                                               -- AGGREGATE  |LOCAL|
-                                                -- IN_MEMORY_STABLE_SORT [$$i(ASC)]  |LOCAL|
+                                                -- MICRO_STABLE_SORT [$$i(ASC)]  |LOCAL|
                                                   -- STREAM_SELECT  |LOCAL|
                                                     -- NESTED_TUPLE_SOURCE  |LOCAL|
                                             }
@@ -113,7 +113,7 @@
                                         -- PRE_CLUSTERED_GROUP_BY[$$129]  |PARTITIONED|
                                                 {
                                                   -- AGGREGATE  |LOCAL|
-                                                    -- IN_MEMORY_STABLE_SORT [$$i(ASC)]  |LOCAL|
+                                                    -- MICRO_STABLE_SORT [$$i(ASC)]  |LOCAL|
                                                       -- STREAM_SELECT  |LOCAL|
                                                         -- NESTED_TUPLE_SOURCE  |LOCAL|
                                                 }
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/similarity/jaccard-similarity-join-right-ahead.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/similarity/jaccard-similarity-join-right-ahead.plan
index ab700b6..cd036ff 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/similarity/jaccard-similarity-join-right-ahead.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/similarity/jaccard-similarity-join-right-ahead.plan
@@ -23,7 +23,7 @@
                                     -- PRE_CLUSTERED_GROUP_BY[$$78]  |PARTITIONED|
                                             {
                                               -- AGGREGATE  |LOCAL|
-                                                -- IN_MEMORY_STABLE_SORT [$$i(ASC)]  |LOCAL|
+                                                -- MICRO_STABLE_SORT [$$i(ASC)]  |LOCAL|
                                                   -- STREAM_SELECT  |LOCAL|
                                                     -- NESTED_TUPLE_SOURCE  |LOCAL|
                                             }
@@ -80,7 +80,7 @@
                                         -- PRE_CLUSTERED_GROUP_BY[$$80]  |PARTITIONED|
                                                 {
                                                   -- AGGREGATE  |LOCAL|
-                                                    -- IN_MEMORY_STABLE_SORT [$$i(ASC)]  |LOCAL|
+                                                    -- MICRO_STABLE_SORT [$$i(ASC)]  |LOCAL|
                                                       -- STREAM_SELECT  |LOCAL|
                                                         -- NESTED_TUPLE_SOURCE  |LOCAL|
                                                 }
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/udfs/query-ASTERIXDB-1308-1.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/udfs/query-ASTERIXDB-1308-1.plan
index f86825e..6e92aec 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/udfs/query-ASTERIXDB-1308-1.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/udfs/query-ASTERIXDB-1308-1.plan
@@ -10,7 +10,7 @@
                   -- SUBPLAN  |UNPARTITIONED|
                           {
                             -- AGGREGATE  |UNPARTITIONED|
-                              -- IN_MEMORY_STABLE_SORT [$$j(ASC)]  |UNPARTITIONED|
+                              -- MICRO_STABLE_SORT [$$j(ASC)]  |UNPARTITIONED|
                                 -- UNNEST  |UNPARTITIONED|
                                   -- NESTED_TUPLE_SOURCE  |UNPARTITIONED|
                           }
@@ -28,7 +28,7 @@
                                                 -- AGGREGATE  |LOCAL|
                                                   -- STREAM_SELECT  |UNPARTITIONED|
                                                     -- RUNNING_AGGREGATE  |UNPARTITIONED|
-                                                      -- IN_MEMORY_STABLE_SORT [$$j(ASC)]  |UNPARTITIONED|
+                                                      -- MICRO_STABLE_SORT [$$j(ASC)]  |UNPARTITIONED|
                                                         -- UNNEST  |UNPARTITIONED|
                                                           -- NESTED_TUPLE_SOURCE  |UNPARTITIONED|
                                             }
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/udfs/query-ASTERIXDB-1308-2.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/udfs/query-ASTERIXDB-1308-2.plan
index 2eb7603..0c0b45d 100644
--- a/asterixdb/asterix-app/src/test/resources/optimizerts/results/udfs/query-ASTERIXDB-1308-2.plan
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/udfs/query-ASTERIXDB-1308-2.plan
@@ -12,7 +12,7 @@
                             -- SUBPLAN  |LOCAL|
                                     {
                                       -- AGGREGATE  |LOCAL|
-                                        -- IN_MEMORY_STABLE_SORT [$$j(ASC)]  |LOCAL|
+                                        -- MICRO_STABLE_SORT [$$j(ASC)]  |LOCAL|
                                           -- UNNEST  |LOCAL|
                                             -- NESTED_TUPLE_SOURCE  |LOCAL|
                                     }
@@ -22,7 +22,7 @@
               -- SUBPLAN  |PARTITIONED|
                       {
                         -- AGGREGATE  |LOCAL|
-                          -- IN_MEMORY_STABLE_SORT [$$98(ASC)]  |LOCAL|
+                          -- MICRO_STABLE_SORT [$$98(ASC)]  |LOCAL|
                             -- ASSIGN  |LOCAL|
                               -- UNNEST  |LOCAL|
                                 -- NESTED_TUPLE_SOURCE  |LOCAL|
@@ -41,7 +41,7 @@
                                     -- SUBPLAN  |LOCAL|
                                             {
                                               -- AGGREGATE  |LOCAL|
-                                                -- IN_MEMORY_STABLE_SORT [$$j(ASC)]  |LOCAL|
+                                                -- MICRO_STABLE_SORT [$$j(ASC)]  |LOCAL|
                                                   -- UNNEST  |LOCAL|
                                                     -- NESTED_TUPLE_SOURCE  |LOCAL|
                                             }
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/sorting/micro_external_sort/micro_external_sort.1.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/sorting/micro_external_sort/micro_external_sort.1.query.sqlpp
new file mode 100644
index 0000000..7d100cd
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/sorting/micro_external_sort/micro_external_sort.1.query.sqlpp
@@ -0,0 +1,52 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+// testing micro external sort in a subplan that generates runs and merges them
+drop dataverse test if exists;
+create dataverse test;
+use test;
+
+set `compiler.sortmemory` "130KB";
+
+with ds AS (
+from range(0,89999) i
+select value {"id": i, "a":
+CASE ( i % 3)
+WHEN 0 THEN "one"
+WHEN 1 THEN "two"
+WHEN 2 THEN "three"
+END,
+"b": CASE ( (i div 3) % 3)
+WHEN 0 THEN "SUM_1s"
+WHEN 1 THEN "SUM_2s"
+WHEN 2 THEN "SUM_3s" END,
+"c": CASE ((i div 3) % 3)
+WHEN 0 THEN 1
+WHEN 1 THEN 2
+WHEN 2 THEN 3 END})
+SELECT `group`,
+(SELECT group_num, sum(g.d.c) AS sum
+FROM g
+GROUP BY g.d.b AS group_num
+ORDER BY sum
+) AS sum_per_group
+FROM ds d
+GROUP BY d.a AS `group`
+GROUP AS g
+ORDER BY `group`;
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/sorting/micro_external_sort/micro_external_sort.1.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/sorting/micro_external_sort/micro_external_sort.1.adm
new file mode 100644
index 0000000..6d57f23
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/sorting/micro_external_sort/micro_external_sort.1.adm
@@ -0,0 +1,3 @@
+{ "group": "one", "sum_per_group": [ { "group_num": "SUM_1s", "sum": 10000 }, { "group_num": "SUM_2s", "sum": 20000 }, { "group_num": "SUM_3s", "sum": 30000 } ] }
+{ "group": "three", "sum_per_group": [ { "group_num": "SUM_1s", "sum": 10000 }, { "group_num": "SUM_2s", "sum": 20000 }, { "group_num": "SUM_3s", "sum": 30000 } ] }
+{ "group": "two", "sum_per_group": [ { "group_num": "SUM_1s", "sum": 10000 }, { "group_num": "SUM_2s", "sum": 20000 }, { "group_num": "SUM_3s", "sum": 30000 } ] }
\ No newline at end of file
diff --git a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/base/PhysicalOperatorTag.java b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/base/PhysicalOperatorTag.java
index 404a8dc..8e1f77f 100644
--- a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/base/PhysicalOperatorTag.java
+++ b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/base/PhysicalOperatorTag.java
@@ -36,7 +36,7 @@
     HDFS_READER,
     HYBRID_HASH_JOIN,
     IN_MEMORY_HASH_JOIN,
-    IN_MEMORY_STABLE_SORT,
+    MICRO_STABLE_SORT,
     INDEX_BULKLOAD,
     INDEX_INSERT_DELETE,
     INSERT_DELETE,
diff --git a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/AbstractStableSortPOperator.java b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/AbstractStableSortPOperator.java
index 0c08369..81852d4 100644
--- a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/AbstractStableSortPOperator.java
+++ b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/AbstractStableSortPOperator.java
@@ -49,10 +49,12 @@
 
 public abstract class AbstractStableSortPOperator extends AbstractPhysicalOperator {
 
-    protected OrderColumn[] sortColumns;
-    protected ILocalStructuralProperty orderProp;
+    final int maxNumberOfFrames;
+    OrderColumn[] sortColumns;
+    ILocalStructuralProperty orderProp;
 
-    public AbstractStableSortPOperator() {
+    AbstractStableSortPOperator(int maxNumberOfFrames) {
+        this.maxNumberOfFrames = maxNumberOfFrames;
     }
 
     public OrderColumn[] getSortColumns() {
diff --git a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/InMemoryStableSortPOperator.java b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/MicroStableSortPOperator.java
similarity index 93%
rename from hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/InMemoryStableSortPOperator.java
rename to hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/MicroStableSortPOperator.java
index d304421..c6a7d9d 100644
--- a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/InMemoryStableSortPOperator.java
+++ b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/MicroStableSortPOperator.java
@@ -37,14 +37,15 @@
 import org.apache.hyracks.api.dataflow.value.INormalizedKeyComputerFactory;
 import org.apache.hyracks.api.dataflow.value.RecordDescriptor;
 
-public class InMemoryStableSortPOperator extends AbstractStableSortPOperator {
+public class MicroStableSortPOperator extends AbstractStableSortPOperator {
 
-    public InMemoryStableSortPOperator() {
+    public MicroStableSortPOperator(int maxNumberOfFrames) {
+        super(maxNumberOfFrames);
     }
 
     @Override
     public PhysicalOperatorTag getOperatorTag() {
-        return PhysicalOperatorTag.IN_MEMORY_STABLE_SORT;
+        return PhysicalOperatorTag.MICRO_STABLE_SORT;
     }
 
     @Override
@@ -79,7 +80,7 @@
             i++;
         }
 
-        IPushRuntimeFactory runtime = new InMemorySortRuntimeFactory(sortFields, nkcf, comps, null);
+        IPushRuntimeFactory runtime = new InMemorySortRuntimeFactory(sortFields, nkcf, comps, null, maxNumberOfFrames);
         builder.contributeMicroOperator(op, runtime, recDescriptor);
         ILogicalOperator src = op.getInputs().get(0).getValue();
         builder.contributeGraphEdge(src, 0, op, 0);
diff --git a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/StableSortPOperator.java b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/StableSortPOperator.java
index d13c51a..9567e5b 100644
--- a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/StableSortPOperator.java
+++ b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/StableSortPOperator.java
@@ -47,16 +47,14 @@
 
 public class StableSortPOperator extends AbstractStableSortPOperator {
 
-    private int maxNumberOfFrames;
-    private int topK;
+    private final int topK;
 
     public StableSortPOperator(int maxNumberOfFrames) {
         this(maxNumberOfFrames, -1);
     }
 
     public StableSortPOperator(int maxNumberOfFrames, int topK) {
-        super();
-        this.maxNumberOfFrames = maxNumberOfFrames;
+        super(maxNumberOfFrames);
         this.topK = topK;
     }
 
@@ -86,6 +84,7 @@
 
         IVariableTypeEnvironment env = context.getTypeEnvironment(op);
         int i = 0;
+        // TODO(ali): should refactor common code with micro sort op
         for (OrderColumn oc : sortColumns) {
             LogicalVariable var = oc.getColumn();
             sortFields[i] = opSchema.findVariable(var);
diff --git a/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/EnforceStructuralPropertiesRule.java b/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/EnforceStructuralPropertiesRule.java
index 67c1f1d..a011abf 100644
--- a/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/EnforceStructuralPropertiesRule.java
+++ b/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/EnforceStructuralPropertiesRule.java
@@ -66,7 +66,7 @@
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.BroadcastExchangePOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.HashPartitionExchangePOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.HashPartitionMergeExchangePOperator;
-import org.apache.hyracks.algebricks.core.algebra.operators.physical.InMemoryStableSortPOperator;
+import org.apache.hyracks.algebricks.core.algebra.operators.physical.MicroStableSortPOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.OneToOneExchangePOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.RandomMergeExchangePOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.RandomPartitionExchangePOperator;
@@ -449,7 +449,7 @@
         AbstractLogicalOperator op = (AbstractLogicalOperator) opRef.getValue();
         if (op.getOperatorTag() != LogicalOperatorTag.ORDER
                 || (op.getPhysicalOperator().getOperatorTag() != PhysicalOperatorTag.STABLE_SORT
-                        && op.getPhysicalOperator().getOperatorTag() != PhysicalOperatorTag.IN_MEMORY_STABLE_SORT)
+                        && op.getPhysicalOperator().getOperatorTag() != PhysicalOperatorTag.MICRO_STABLE_SORT)
                 || delivered.getLocalProperties() == null) {
             return false;
         }
@@ -555,7 +555,7 @@
         oo.setSourceLocation(sourceLoc);
         oo.setExecutionMode(AbstractLogicalOperator.ExecutionMode.LOCAL);
         if (isMicroOp) {
-            oo.setPhysicalOperator(new InMemoryStableSortPOperator());
+            oo.setPhysicalOperator(new MicroStableSortPOperator(physicalOptimizationConfig.getMaxFramesExternalSort()));
         } else {
             oo.setPhysicalOperator(new StableSortPOperator(physicalOptimizationConfig.getMaxFramesExternalSort()));
         }
diff --git a/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/PushNestedOrderByUnderPreSortedGroupByRule.java b/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/PushNestedOrderByUnderPreSortedGroupByRule.java
index 5864c3b..344e103 100644
--- a/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/PushNestedOrderByUnderPreSortedGroupByRule.java
+++ b/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/PushNestedOrderByUnderPreSortedGroupByRule.java
@@ -89,7 +89,7 @@
         }
         AbstractPhysicalOperator pOrder1 = (AbstractPhysicalOperator) op2.getPhysicalOperator();
         if (pOrder1.getOperatorTag() != PhysicalOperatorTag.STABLE_SORT
-                && pOrder1.getOperatorTag() != PhysicalOperatorTag.IN_MEMORY_STABLE_SORT) {
+                && pOrder1.getOperatorTag() != PhysicalOperatorTag.MICRO_STABLE_SORT) {
             return false;
         }
         // StableSortPOperator sort1 = (StableSortPOperator) pOrder1;
diff --git a/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/SetAlgebricksPhysicalOperatorsRule.java b/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/SetAlgebricksPhysicalOperatorsRule.java
index 49e5a0b..f127898 100644
--- a/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/SetAlgebricksPhysicalOperatorsRule.java
+++ b/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/SetAlgebricksPhysicalOperatorsRule.java
@@ -86,7 +86,6 @@
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.DistributeResultPOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.EmptyTupleSourcePOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.ExternalGroupByPOperator;
-import org.apache.hyracks.algebricks.core.algebra.operators.physical.InMemoryStableSortPOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.IndexBulkloadPOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.IndexInsertDeleteUpsertPOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.InsertDeleteUpsertPOperator;
@@ -94,6 +93,7 @@
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.LeftOuterUnnestPOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.MicroPreSortedDistinctByPOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.MicroPreclusteredGroupByPOperator;
+import org.apache.hyracks.algebricks.core.algebra.operators.physical.MicroStableSortPOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.MicroUnionAllPOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.NestedTupleSourcePOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.PreSortedDistinctByPOperator;
@@ -271,7 +271,7 @@
             if (topLevelOp) {
                 return new StableSortPOperator(physicalOptimizationConfig.getMaxFramesExternalSort(), oo.getTopK());
             } else {
-                return new InMemoryStableSortPOperator();
+                return new MicroStableSortPOperator(physicalOptimizationConfig.getMaxFramesExternalSort());
             }
         }
 
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/sort/InMemorySortRuntimeFactory.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/sort/InMemorySortRuntimeFactory.java
index 2453029..b34b7b9 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/sort/InMemorySortRuntimeFactory.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/sort/InMemorySortRuntimeFactory.java
@@ -19,39 +19,43 @@
 package org.apache.hyracks.algebricks.runtime.operators.sort;
 
 import java.nio.ByteBuffer;
+import java.util.List;
 
 import org.apache.hyracks.algebricks.common.exceptions.NotImplementedException;
 import org.apache.hyracks.algebricks.runtime.operators.base.AbstractOneInputOneOutputPushRuntime;
 import org.apache.hyracks.algebricks.runtime.operators.base.AbstractOneInputOneOutputRuntimeFactory;
+import org.apache.hyracks.api.comm.IFrameWriter;
 import org.apache.hyracks.api.context.IHyracksTaskContext;
+import org.apache.hyracks.api.dataflow.value.IBinaryComparator;
 import org.apache.hyracks.api.dataflow.value.IBinaryComparatorFactory;
+import org.apache.hyracks.api.dataflow.value.INormalizedKeyComputer;
 import org.apache.hyracks.api.dataflow.value.INormalizedKeyComputerFactory;
 import org.apache.hyracks.api.exceptions.HyracksDataException;
+import org.apache.hyracks.api.resources.IDeallocatable;
 import org.apache.hyracks.api.util.CleanupUtils;
+import org.apache.hyracks.dataflow.common.io.GeneratedRunFileReader;
 import org.apache.hyracks.dataflow.std.buffermanager.EnumFreeSlotPolicy;
-import org.apache.hyracks.dataflow.std.buffermanager.FrameFreeSlotPolicyFactory;
-import org.apache.hyracks.dataflow.std.buffermanager.IFrameBufferManager;
-import org.apache.hyracks.dataflow.std.buffermanager.VariableFrameMemoryManager;
-import org.apache.hyracks.dataflow.std.buffermanager.VariableFramePool;
-import org.apache.hyracks.dataflow.std.sort.FrameSorterMergeSort;
+import org.apache.hyracks.dataflow.std.sort.Algorithm;
+import org.apache.hyracks.dataflow.std.sort.ExternalSortRunGenerator;
+import org.apache.hyracks.dataflow.std.sort.ExternalSortRunMerger;
 
 public class InMemorySortRuntimeFactory extends AbstractOneInputOneOutputRuntimeFactory {
 
     private static final long serialVersionUID = 1L;
-
+    private final int framesLimit;
     private final int[] sortFields;
     private final INormalizedKeyComputerFactory[] keyNormalizerFactories;
     private final IBinaryComparatorFactory[] comparatorFactories;
 
     public InMemorySortRuntimeFactory(int[] sortFields, INormalizedKeyComputerFactory firstKeyNormalizerFactory,
-            IBinaryComparatorFactory[] comparatorFactories, int[] projectionList) {
+            IBinaryComparatorFactory[] comparatorFactories, int[] projectionList, int framesLimit) {
         this(sortFields, firstKeyNormalizerFactory != null
                 ? new INormalizedKeyComputerFactory[] { firstKeyNormalizerFactory } : null, comparatorFactories,
-                projectionList);
+                projectionList, framesLimit);
     }
 
     public InMemorySortRuntimeFactory(int[] sortFields, INormalizedKeyComputerFactory[] keyNormalizerFactories,
-            IBinaryComparatorFactory[] comparatorFactories, int[] projectionList) {
+            IBinaryComparatorFactory[] comparatorFactories, int[] projectionList, int framesLimit) {
         super(projectionList);
         // Obs: the projection list is currently ignored.
         if (projectionList != null) {
@@ -60,52 +64,122 @@
         this.sortFields = sortFields;
         this.keyNormalizerFactories = keyNormalizerFactories;
         this.comparatorFactories = comparatorFactories;
+        this.framesLimit = framesLimit;
     }
 
     @Override
     public AbstractOneInputOneOutputPushRuntime createOneOutputPushRuntime(final IHyracksTaskContext ctx)
             throws HyracksDataException {
-        return new AbstractOneInputOneOutputPushRuntime() {
-            FrameSorterMergeSort frameSorter = null;
+        InMemorySortPushRuntime pushRuntime = new InMemorySortPushRuntime(ctx);
+        ctx.registerDeallocatable(pushRuntime);
+        return pushRuntime;
+    }
 
-            @Override
-            public void open() throws HyracksDataException {
-                super.open();
-                if (frameSorter == null) {
-                    IFrameBufferManager manager = new VariableFrameMemoryManager(
-                            new VariableFramePool(ctx, VariableFramePool.UNLIMITED_MEMORY),
-                            FrameFreeSlotPolicyFactory.createFreeSlotPolicy(EnumFreeSlotPolicy.LAST_FIT));
-                    frameSorter = new FrameSorterMergeSort(ctx, manager, VariableFramePool.UNLIMITED_MEMORY, sortFields,
-                            keyNormalizerFactories, comparatorFactories, outputRecordDesc);
-                }
-                frameSorter.reset();
+    private class InMemorySortPushRuntime extends AbstractOneInputOneOutputPushRuntime implements IDeallocatable {
+        final IHyracksTaskContext ctx;
+        ExternalSortRunGenerator runsGenerator = null;
+        ExternalSortRunMerger runsMerger = null;
+        IFrameWriter wrappingWriter = null;
+
+        private InMemorySortPushRuntime(IHyracksTaskContext ctx) {
+            this.ctx = ctx;
+        }
+
+        @Override
+        public void open() throws HyracksDataException {
+            if (runsGenerator == null) {
+                runsGenerator = new ExternalSortRunGenerator(ctx, sortFields, keyNormalizerFactories,
+                        comparatorFactories, outputRecordDesc, Algorithm.MERGE_SORT, EnumFreeSlotPolicy.LAST_FIT,
+                        framesLimit, Integer.MAX_VALUE);
             }
+            // next writer will be opened later when preparing the merger
+            isOpen = true;
+            runsGenerator.open();
+            runsGenerator.getSorter().reset();
+        }
 
-            @Override
-            public void nextFrame(ByteBuffer buffer) throws HyracksDataException {
-                frameSorter.insertFrame(buffer);
-            }
+        @Override
+        public void nextFrame(ByteBuffer buffer) throws HyracksDataException {
+            runsGenerator.nextFrame(buffer);
+        }
 
-            @Override
-            public void close() throws HyracksDataException {
-                Throwable failure = null;
-                if (isOpen) {
-                    try {
-                        if (!failed) {
-                            frameSorter.sort();
-                            frameSorter.flush(writer);
+        @Override
+        public void close() throws HyracksDataException {
+            Throwable failure = null;
+            if (isOpen) {
+                try {
+                    if (!failed) {
+                        runsGenerator.close();
+                        createOrResetRunsMerger();
+                        if (runsGenerator.getRuns().isEmpty()) {
+                            wrappingWriter = runsMerger.prepareSkipMergingFinalResultWriter(writer);
+                            wrappingWriter.open();
+                            if (runsGenerator.getSorter().hasRemaining()) {
+                                runsGenerator.getSorter().flush(wrappingWriter);
+                            }
+                        } else {
+                            wrappingWriter = runsMerger.prepareFinalMergeResultWriter(writer);
+                            wrappingWriter.open();
+                            runsMerger.process(wrappingWriter);
                         }
+                    }
+                } catch (Throwable th) {
+                    failure = th;
+                    fail(th);
+                } finally {
+                    failure = CleanupUtils.close(wrappingWriter, failure);
+                    wrappingWriter = null;
+                }
+            }
+            isOpen = false;
+            if (failure != null) {
+                throw HyracksDataException.create(failure);
+            }
+        }
+
+        @Override
+        public void fail() throws HyracksDataException {
+            failed = true;
+            // clean up the runs if some have been generated. double close should be idempotent.
+            if (runsGenerator != null) {
+                List<GeneratedRunFileReader> runs = runsGenerator.getRuns();
+                for (int i = 0, size = runs.size(); i < size; i++) {
+                    try {
+                        runs.get(i).close();
                     } catch (Throwable th) {
-                        failure = th;
-                        fail(th);
-                    } finally {
-                        failure = CleanupUtils.close(writer, failure);
+                        // ignore
                     }
                 }
-                if (failure != null) {
-                    throw HyracksDataException.create(failure);
+            }
+            if (wrappingWriter != null) {
+                wrappingWriter.fail();
+            }
+        }
+
+        @Override
+        public void deallocate() {
+            if (runsGenerator != null) {
+                try {
+                    runsGenerator.getSorter().close();
+                } catch (Exception e) {
+                    // ignore
                 }
             }
-        };
+        }
+
+        private void createOrResetRunsMerger() {
+            if (runsMerger == null) {
+                IBinaryComparator[] comparators = new IBinaryComparator[comparatorFactories.length];
+                for (int i = 0; i < comparatorFactories.length; ++i) {
+                    comparators[i] = comparatorFactories[i].createBinaryComparator();
+                }
+                INormalizedKeyComputer nmkComputer =
+                        keyNormalizerFactories == null ? null : keyNormalizerFactories[0].createNormalizedKeyComputer();
+                runsMerger = new ExternalSortRunMerger(ctx, runsGenerator.getRuns(), sortFields, comparators,
+                        nmkComputer, outputRecordDesc, framesLimit, Integer.MAX_VALUE);
+            } else {
+                runsMerger.reset(runsGenerator.getRuns());
+            }
+        }
     }
 }
diff --git a/hyracks-fullstack/algebricks/algebricks-tests/src/test/java/org/apache/hyracks/algebricks/tests/pushruntime/PushRuntimeTest.java b/hyracks-fullstack/algebricks/algebricks-tests/src/test/java/org/apache/hyracks/algebricks/tests/pushruntime/PushRuntimeTest.java
index 99967c1..e9b3fc3 100644
--- a/hyracks-fullstack/algebricks/algebricks-tests/src/test/java/org/apache/hyracks/algebricks/tests/pushruntime/PushRuntimeTest.java
+++ b/hyracks-fullstack/algebricks/algebricks-tests/src/test/java/org/apache/hyracks/algebricks/tests/pushruntime/PushRuntimeTest.java
@@ -720,7 +720,7 @@
         // the algebricks op.
         InMemorySortRuntimeFactory sort =
                 new InMemorySortRuntimeFactory(new int[] { 1 }, (INormalizedKeyComputerFactory) null,
-                        new IBinaryComparatorFactory[] { UTF8StringBinaryComparatorFactory.INSTANCE }, null);
+                        new IBinaryComparatorFactory[] { UTF8StringBinaryComparatorFactory.INSTANCE }, null, 50);
         RecordDescriptor sortDesc = scannerDesc;
 
         String fileName = "scanMicroSortWrite.out";
@@ -836,7 +836,7 @@
         RecordDescriptor sortDesc = scannerDesc;
         InMemorySortRuntimeFactory sort =
                 new InMemorySortRuntimeFactory(new int[] { 3 }, (INormalizedKeyComputerFactory) null,
-                        new IBinaryComparatorFactory[] { IntegerBinaryComparatorFactory.INSTANCE }, null);
+                        new IBinaryComparatorFactory[] { IntegerBinaryComparatorFactory.INSTANCE }, null, 50);
 
         // the group-by
         NestedTupleSourceRuntimeFactory nts = new NestedTupleSourceRuntimeFactory();
diff --git a/hyracks-fullstack/hyracks/hyracks-dataflow-std/src/main/java/org/apache/hyracks/dataflow/std/sort/AbstractExternalSortRunMerger.java b/hyracks-fullstack/hyracks/hyracks-dataflow-std/src/main/java/org/apache/hyracks/dataflow/std/sort/AbstractExternalSortRunMerger.java
index e860288..08b2303 100644
--- a/hyracks-fullstack/hyracks/hyracks-dataflow-std/src/main/java/org/apache/hyracks/dataflow/std/sort/AbstractExternalSortRunMerger.java
+++ b/hyracks-fullstack/hyracks/hyracks-dataflow-std/src/main/java/org/apache/hyracks/dataflow/std/sort/AbstractExternalSortRunMerger.java
@@ -36,6 +36,7 @@
 import org.apache.hyracks.dataflow.common.io.RunFileReader;
 import org.apache.hyracks.dataflow.common.io.RunFileWriter;
 import org.apache.hyracks.dataflow.std.sort.util.GroupVSizeFrame;
+import org.apache.hyracks.util.annotations.CriticalPath;
 import org.apache.logging.log4j.Level;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -48,10 +49,12 @@
     private final IBinaryComparator[] comparators;
     private final INormalizedKeyComputer nmkComputer;
     private final RecordDescriptor recordDesc;
-    private final int framesLimit;
+    private final int maxMergeWidth;
     private final int topK;
+    private List<GeneratedRunFileReader> partialRuns;
     private List<GroupVSizeFrame> inFrames;
     private VSizeFrame outputFrame;
+    private boolean first;
     private static final Logger LOGGER = LogManager.getLogger();
 
     public AbstractExternalSortRunMerger(IHyracksTaskContext ctx, List<GeneratedRunFileReader> runs,
@@ -69,16 +72,15 @@
         this.comparators = comparators;
         this.nmkComputer = nmkComputer;
         this.recordDesc = recordDesc;
-        this.framesLimit = framesLimit;
+        this.maxMergeWidth = framesLimit - 1;
         this.topK = topK;
+        this.first = true;
     }
 
+    @CriticalPath
     public void process(IFrameWriter finalWriter) throws HyracksDataException {
         try {
-            int maxMergeWidth = framesLimit - 1;
-            inFrames = new ArrayList<>(maxMergeWidth);
-            outputFrame = new VSizeFrame(ctx);
-            List<GeneratedRunFileReader> partialRuns = new ArrayList<>(maxMergeWidth);
+            createReusableObjects();
             int stop = runs.size();
             currentGenerationRunAvailable.set(0, stop);
             int numberOfPasses = 1;
@@ -210,6 +212,21 @@
         }
     }
 
+    public void reset(List<GeneratedRunFileReader> newRuns) {
+        this.runs.clear();
+        this.runs.addAll(newRuns);
+        this.currentGenerationRunAvailable.clear();
+    }
+
+    private void createReusableObjects() throws HyracksDataException {
+        if (first) {
+            first = false;
+            inFrames = new ArrayList<>(maxMergeWidth);
+            outputFrame = new VSizeFrame(ctx);
+            partialRuns = new ArrayList<>(maxMergeWidth);
+        }
+    }
+
     public abstract IFrameWriter prepareSkipMergingFinalResultWriter(IFrameWriter nextWriter)
             throws HyracksDataException;