Fix some oversights in BRIN patch.

Remove HeapScanDescData.rs_initblock, which wasn't being used for anything
in the final version of the patch.

Fix IndexBuildHeapScan so that it supports syncscan again; the patch
broke synchronous scanning for index builds by forcing rs_startblk
to zero even when the caller did not care about that and had asked
for syncscan.

Add some commentary and usage defenses to heap_setscanlimits().

Fix heapam so that asking for rs_numblocks == 0 does what you would
reasonably expect.  As coded it amounted to requesting a whole-table
scan, because those "--x <= 0" tests on an unsigned variable would
behave surprisingly.

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 86a2e6bae6abdb5fdc62f1a2078f645111abc8a4..6f4ff2718fed8d224837d2aeb46da44cb5cadecd 100644 (file)
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -277,7 +277,6 @@ initscan(HeapScanDesc scan, ScanKey key, bool is_rescan)
        scan->rs_startblock = 0;
    }
 
-   scan->rs_initblock = 0;
    scan->rs_numblocks = InvalidBlockNumber;
    scan->rs_inited = false;
    scan->rs_ctup.t_data = NULL;
@@ -302,11 +301,22 @@ initscan(HeapScanDesc scan, ScanKey key, bool is_rescan)
        pgstat_count_heap_scan(scan->rs_rd);
 }
 
+/*
+ * heap_setscanlimits - restrict range of a heapscan
+ *
+ * startBlk is the page to start at
+ * numBlks is number of pages to scan (InvalidBlockNumber means "all")
+ */
 void
 heap_setscanlimits(HeapScanDesc scan, BlockNumber startBlk, BlockNumber numBlks)
 {
+   Assert(!scan->rs_inited);   /* else too late to change */
+   Assert(!scan->rs_syncscan); /* else rs_startblock is significant */
+
+   /* Check startBlk is valid (but allow case of zero blocks...) */
+   Assert(startBlk == 0 || startBlk < scan->rs_nblocks);
+
    scan->rs_startblock = startBlk;
-   scan->rs_initblock = startBlk;
    scan->rs_numblocks = numBlks;
 }
 
@@ -477,7 +487,7 @@ heapgettup(HeapScanDesc scan,
            /*
             * return null immediately if relation is empty
             */
-           if (scan->rs_nblocks == 0)
+           if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
            {
                Assert(!BufferIsValid(scan->rs_cbuf));
                tuple->t_data = NULL;
@@ -511,7 +521,7 @@ heapgettup(HeapScanDesc scan,
            /*
             * return null immediately if relation is empty
             */
-           if (scan->rs_nblocks == 0)
+           if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
            {
                Assert(!BufferIsValid(scan->rs_cbuf));
                tuple->t_data = NULL;
@@ -651,7 +661,7 @@ heapgettup(HeapScanDesc scan,
        if (backward)
        {
            finished = (page == scan->rs_startblock) ||
-               (scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks <= 0 : false);
+               (scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks == 0 : false);
            if (page == 0)
                page = scan->rs_nblocks;
            page--;
@@ -662,7 +672,7 @@ heapgettup(HeapScanDesc scan,
            if (page >= scan->rs_nblocks)
                page = 0;
            finished = (page == scan->rs_startblock) ||
-               (scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks <= 0 : false);
+               (scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks == 0 : false);
 
            /*
             * Report our new scan position for synchronization purposes. We
@@ -754,7 +764,7 @@ heapgettup_pagemode(HeapScanDesc scan,
            /*
             * return null immediately if relation is empty
             */
-           if (scan->rs_nblocks == 0)
+           if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
            {
                Assert(!BufferIsValid(scan->rs_cbuf));
                tuple->t_data = NULL;
@@ -785,7 +795,7 @@ heapgettup_pagemode(HeapScanDesc scan,
            /*
             * return null immediately if relation is empty
             */
-           if (scan->rs_nblocks == 0)
+           if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
            {
                Assert(!BufferIsValid(scan->rs_cbuf));
                tuple->t_data = NULL;
@@ -914,7 +924,7 @@ heapgettup_pagemode(HeapScanDesc scan,
        if (backward)
        {
            finished = (page == scan->rs_startblock) ||
-               (scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks <= 0 : false);
+               (scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks == 0 : false);
            if (page == 0)
                page = scan->rs_nblocks;
            page--;
@@ -925,7 +935,7 @@ heapgettup_pagemode(HeapScanDesc scan,
            if (page >= scan->rs_nblocks)
                page = 0;
            finished = (page == scan->rs_startblock) ||
-               (scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks <= 0 : false);
+               (scan->rs_numblocks != InvalidBlockNumber ? --scan->rs_numblocks == 0 : false);
 
            /*
             * Report our new scan position for synchronization purposes. We

diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 4246554d19d21fb5da4c6369f24d71c86b6c5059..69f35c933097920c3a0da919e8a9ef7ff6563fec 100644 (file)
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -2168,7 +2168,8 @@ IndexBuildHeapScan(Relation heapRelation,
 /*
  * As above, except that instead of scanning the complete heap, only the given
  * number of blocks are scanned.  Scan to end-of-rel can be signalled by
- * passing InvalidBlockNumber as numblocks.
+ * passing InvalidBlockNumber as numblocks.  Note that restricting the range
+ * to scan cannot be done when requesting syncscan.
  */
 double
 IndexBuildHeapRangeScan(Relation heapRelation,
@@ -2251,7 +2252,14 @@ IndexBuildHeapRangeScan(Relation heapRelation,
                                allow_sync);    /* syncscan OK? */
 
    /* set our scan endpoints */
-   heap_setscanlimits(scan, start_blockno, numblocks);
+   if (!allow_sync)
+       heap_setscanlimits(scan, start_blockno, numblocks);
+   else
+   {
+       /* syncscan can only be requested on whole relation */
+       Assert(start_blockno == 0);
+       Assert(numblocks == InvalidBlockNumber);
+   }
 
    reltuples = 0;
 

diff --git a/src/include/access/relscan.h b/src/include/access/relscan.h
index f2482e99d6c56e12eec3ba97b65766ce59c5291e..6e6231971fdca3ef0a780f179b7cda515b4835a3 100644 (file)
--- a/src/include/access/relscan.h
+++ b/src/include/access/relscan.h
@@ -38,8 +38,8 @@ typedef struct HeapScanDescData
    /* state set up at initscan time */
    BlockNumber rs_nblocks;     /* total number of blocks in rel */
    BlockNumber rs_startblock;  /* block # to start at */
-   BlockNumber rs_initblock;   /* block # to consider initial of rel */
-   BlockNumber rs_numblocks;   /* number of blocks to scan */
+   BlockNumber rs_numblocks;   /* max number of blocks to scan */
+   /* rs_numblocks is usually InvalidBlockNumber, meaning "scan whole rel" */
    BufferAccessStrategy rs_strategy;   /* access strategy for reads */
    bool        rs_syncscan;    /* report location to syncscan logic? */