Instrument index-only scans to count heap fetches performed.

Patch by me; review by Tom Lane, Jeff Davis, and Peter Geoghegan.

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 8b48105974f8a288988e9170864c9595023aeda0..e297e9cfb9079be18500d8e425ee6cdfa0f731be 100644 (file)
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -1012,6 +1012,9 @@ ExplainNode(PlanState *planstate, List *ancestors,
                        if (plan->qual)
                                show_instrumentation_count("Rows Removed by Filter", 1,
                                                                                   planstate, es);
+                       if (es->analyze)
+                               ExplainPropertyLong("Heap Fetches",
+                                       ((IndexOnlyScanState *) planstate)->ioss_HeapFetches, es);
                        break;
                case T_BitmapIndexScan:
                        show_scan_qual(((BitmapIndexScan *) plan)->indexqualorig,

diff --git a/src/backend/executor/nodeIndexonlyscan.c b/src/backend/executor/nodeIndexonlyscan.c
index 7f1100e15e4352d988f2ea2dd904e67332197d92..4abd805aa31733fafc0b18e80a65c4f91695fae5 100644 (file)
--- a/src/backend/executor/nodeIndexonlyscan.c
+++ b/src/backend/executor/nodeIndexonlyscan.c
@@ -90,6 +90,7 @@ IndexOnlyNext(IndexOnlyScanState *node)
                        /*
                         * Rats, we have to visit the heap to check visibility.
                         */
+                       node->ioss_HeapFetches++;
                        tuple = index_fetch_heap(scandesc);
                        if (tuple == NULL)
                                continue;       /* no visible tuple, try next index entry */
@@ -346,6 +347,7 @@ ExecInitIndexOnlyScan(IndexOnlyScan *node, EState *estate, int eflags)
        indexstate = makeNode(IndexOnlyScanState);
        indexstate->ss.ps.plan = (Plan *) node;
        indexstate->ss.ps.state = estate;
+       indexstate->ioss_HeapFetches = 0;
 
        /*
         * Miscellaneous initialization

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index da4b695cd642b5f3ba0a14695e2db9e29487bb6d..5207102f6c9e79c969c0c5f2b46df4a9800ca452 100644 (file)
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1260,6 +1260,7 @@ typedef struct IndexScanState
  *             RelationDesc       index relation descriptor
  *             ScanDesc                   index scan descriptor
  *             VMBuffer                   buffer in use for visibility map testing, if any
+ *             HeapFetches                number of tuples we were forced to fetch from heap
  * ----------------
  */
 typedef struct IndexOnlyScanState
@@ -1277,6 +1278,7 @@ typedef struct IndexOnlyScanState
        Relation        ioss_RelationDesc;
        IndexScanDesc ioss_ScanDesc;
        Buffer          ioss_VMBuffer;
+       long            ioss_HeapFetches;
 } IndexOnlyScanState;
 
 /* ----------------