Arrange for hash join to skip scanning the outer relation if it detects

that the inner one is completely empty.  Per recent discussion.  Also some
cosmetic cleanups in nearby code.

diff --git a/src/backend/executor/nodeHash.c b/src/backend/executor/nodeHash.c
index c4236f5fcc41175ff70e39875b1c0e8ecb148a5a..5beb6359a8317168a7358d262e8798bc88dce5d2 100644 (file)
--- a/src/backend/executor/nodeHash.c
+++ b/src/backend/executor/nodeHash.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/executor/nodeHash.c,v 1.86 2004/08/29 04:12:31 momjian Exp $
+ *   $PostgreSQL: pgsql/src/backend/executor/nodeHash.c,v 1.87 2004/09/22 19:13:49 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -32,8 +32,8 @@
 /* ----------------------------------------------------------------
  *     ExecHash
  *
- *     build hash table for hashjoin, all do partitioning if more
- *     than one batches are required.
+ *     build hash table for hashjoin, doing partitioning if more
+ *     than one batch is required.
  * ----------------------------------------------------------------
  */
 TupleTableSlot *
@@ -81,6 +81,7 @@ ExecHash(HashState *node)
        slot = ExecProcNode(outerNode);
        if (TupIsNull(slot))
            break;
+       hashtable->hashNonEmpty = true;
        econtext->ecxt_innertuple = slot;
        ExecHashTableInsert(hashtable, econtext, hashkeys);
        ExecClearTuple(slot);
@@ -189,7 +190,7 @@ ExecEndHash(HashState *node)
 /* ----------------------------------------------------------------
  *     ExecHashTableCreate
  *
- *     create a hashtable in shared memory for hashjoin.
+ *     create an empty hashtable data structure for hashjoin.
  * ----------------------------------------------------------------
  */
 HashJoinTable
@@ -226,12 +227,13 @@ ExecHashTableCreate(Hash *node, List *hashOperators)
     * The hashtable control block is just palloc'd from the executor's
     * per-query memory context.
     */
-   hashtable = (HashJoinTable) palloc(sizeof(HashTableData));
+   hashtable = (HashJoinTable) palloc(sizeof(HashJoinTableData));
    hashtable->nbuckets = nbuckets;
    hashtable->totalbuckets = totalbuckets;
    hashtable->buckets = NULL;
    hashtable->nbatch = nbatch;
    hashtable->curbatch = 0;
+   hashtable->hashNonEmpty = false;
    hashtable->innerBatchFile = NULL;
    hashtable->outerBatchFile = NULL;
    hashtable->innerBatchSize = NULL;

diff --git a/src/backend/executor/nodeHashjoin.c b/src/backend/executor/nodeHashjoin.c
index 53215be6e9184702608b6bdcea1cef0e3f157223..294f481cdf5eda8967ade35e50eb9cc3298beab8 100644 (file)
--- a/src/backend/executor/nodeHashjoin.c
+++ b/src/backend/executor/nodeHashjoin.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/executor/nodeHashjoin.c,v 1.65 2004/09/17 18:28:53 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/executor/nodeHashjoin.c,v 1.66 2004/09/22 19:13:49 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -127,6 +127,17 @@ ExecHashJoin(HashJoinState *node)
        hashNode->hashtable = hashtable;
        (void) ExecProcNode((PlanState *) hashNode);
 
+       /*
+        * If the inner relation is completely empty, and we're not doing
+        * an outer join, we can quit without scanning the outer relation.
+        */
+       if (!hashtable->hashNonEmpty && node->js.jointype != JOIN_LEFT)
+       {
+           ExecHashTableDestroy(hashtable);
+           node->hj_HashTable = NULL;
+           return NULL;
+       }
+
        /*
         * Open temp files for outer batches, if needed. Note that file
         * buffers are palloc'd in regular executor context.
@@ -138,10 +149,8 @@ ExecHashJoin(HashJoinState *node)
    }
 
    /*
-    * Now get an outer tuple and probe into the hash table for matches
+    * run the hash join process
     */
-   outerTupleSlot = node->js.ps.ps_OuterTupleSlot;
-
    for (;;)
    {
        /*
@@ -226,7 +235,7 @@ ExecHashJoin(HashJoinState *node)
             * Only the joinquals determine MatchedOuter status, but all
             * quals must pass to actually return the tuple.
             */
-           if (ExecQual(joinqual, econtext, false))
+           if (joinqual == NIL || ExecQual(joinqual, econtext, false))
            {
                node->hj_MatchedOuter = true;
 

diff --git a/src/include/executor/hashjoin.h b/src/include/executor/hashjoin.h
index 5dd6c5c8fe21f14d22ba02ea79fcdbcb242e4fb5..8a2eba8e0bce808c4b258d65fa380e05e3f5f909 100644 (file)
--- a/src/include/executor/hashjoin.h
+++ b/src/include/executor/hashjoin.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/executor/hashjoin.h,v 1.32 2004/08/29 04:13:06 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/executor/hashjoin.h,v 1.33 2004/09/22 19:13:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -47,7 +47,7 @@ typedef struct HashJoinTupleData
 
 typedef HashJoinTupleData *HashJoinTuple;
 
-typedef struct HashTableData
+typedef struct HashJoinTableData
 {
    int         nbuckets;       /* buckets in use during this batch */
    int         totalbuckets;   /* total number of (virtual) buckets */
@@ -57,6 +57,8 @@ typedef struct HashTableData
    int         nbatch;         /* number of batches; 0 means 1-pass join */
    int         curbatch;       /* current batch #, or 0 during 1st pass */
 
+   bool        hashNonEmpty;   /* did inner plan produce any rows? */
+
    /*
     * all these arrays are allocated for the life of the hash join, but
     * only if nbatch > 0:
@@ -90,8 +92,8 @@ typedef struct HashTableData
 
    MemoryContext hashCxt;      /* context for whole-hash-join storage */
    MemoryContext batchCxt;     /* context for this-batch-only storage */
-} HashTableData;
+} HashJoinTableData;
 
-typedef HashTableData *HashJoinTable;
+typedef HashJoinTableData *HashJoinTable;
 
 #endif   /* HASHJOIN_H */