aio: bitmap heap scan: Minimal and hacky improvement for prefetching.

Author:
Reviewed-By:
Discussion: https://postgr.es/m/
Backpatch:

diff --git a/src/backend/executor/nodeBitmapHeapscan.c b/src/backend/executor/nodeBitmapHeapscan.c
index 2db1914affb3b29c5a58bfa8d7eb31caed5a8ae5..3861bd8a24ae84f6e550b4a25977148465ad074e 100644 (file)
--- a/src/backend/executor/nodeBitmapHeapscan.c
+++ b/src/backend/executor/nodeBitmapHeapscan.c
@@ -45,6 +45,7 @@
 #include "executor/nodeBitmapHeapscan.h"
 #include "miscadmin.h"
 #include "pgstat.h"
+#include "storage/aio.h"
 #include "storage/bufmgr.h"
 #include "storage/predicate.h"
 #include "utils/memutils.h"
@@ -463,8 +464,15 @@ BitmapAdjustPrefetchTarget(BitmapHeapScanState *node)
 static inline void
 BitmapPrefetch(BitmapHeapScanState *node, TableScanDesc scan)
 {
+   /*
+    * FIXME: This really should just all be replaced by using one iterator
+    * and a PgStreamingRead. tbm_iterate() actually does a fair bit of work,
+    * we don't want to repeat that. Nor is it good to do the buffer mapping
+    * lookups twice.
+    */
 #ifdef USE_PREFETCH
    ParallelBitmapHeapState *pstate = node->pstate;
+   bool        issued_prefetch = false;
 
    if (pstate == NULL)
    {
@@ -504,7 +512,10 @@ BitmapPrefetch(BitmapHeapScanState *node, TableScanDesc scan)
                                             &node->pvmbuffer));
 
                if (!skip_fetch)
+               {
                    PrefetchBuffer(scan->rs_rd, MAIN_FORKNUM, tbmpre->blockno);
+                   issued_prefetch = true;
+               }
            }
        }
 
@@ -555,10 +566,21 @@ BitmapPrefetch(BitmapHeapScanState *node, TableScanDesc scan)
                                             &node->pvmbuffer));
 
                if (!skip_fetch)
+               {
                    PrefetchBuffer(scan->rs_rd, MAIN_FORKNUM, tbmpre->blockno);
+                   issued_prefetch = true;
+               }
            }
        }
    }
+
+   /*
+    * The PrefetchBuffer() calls staged IOs, but didn't necessarily submit
+    * them, as it is more efficient to amortize the syscall cost across
+    * multiple calls.
+    */
+   if (issued_prefetch)
+       pgaio_submit_pending(true);
 #endif                         /* USE_PREFETCH */
 }