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Commitfce17e4

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Fix CLUSTER progress reporting of number of blocks scanned.
Previously pg_stat_progress_cluster view reported the current blocknumber in heap scan as the number of heap blocks scanned (i.e.,heap_blks_scanned). This reported number could be incorrect whensynchronize_seqscans is enabled, because it allowed the heap scan tostart at block in middle. This could result in wraparounds in theheap_blks_scanned column when the heap scan wrapped around.This commit fixes the bug by calculating the number of blocks fromthe block that the heap scan starts at to the current block in scan,and reporting that number in the heap_blks_scanned column.Also, in pg_stat_progress_cluster view, previously heap_blks_scannedcould not reach heap_blks_total at the end of heap scan phaseif the last pages scanned were empty. This commit fixes the bug bymanually updating heap_blks_scanned to the same value asheap_blks_total when the heap scan phase finishes.Back-patch to v12 where pg_stat_progress_cluster view was introduced.Reported-by: Matthias van de MeentAuthor: Matthias van de MeentReviewed-by: Fujii MasaoDiscussion:https://postgr.es/m/CAEze2WjCBWSGkVfYag001Rc4+-nNLDpWM7QbyD6yPvuhKs-gYQ@mail.gmail.com
1 parentea7a167 commitfce17e4

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‎src/backend/access/heap/heapam_handler.c

Lines changed: 27 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -712,6 +712,7 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
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Datum*values;
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bool*isnull;
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BufferHeapTupleTableSlot*hslot;
715+
BlockNumberprev_cblock=InvalidBlockNumber;
715716

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/* Remember if it's a system catalog */
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is_system_catalog=IsSystemRelation(OldHeap);
@@ -810,14 +811,38 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
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else
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{
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if (!table_scan_getnextslot(tableScan,ForwardScanDirection,slot))
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{
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/*
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* If the last pages of the scan were empty, we would go to
817+
* the next phase while heap_blks_scanned != heap_blks_total.
818+
* Instead, to ensure that heap_blks_scanned is equivalent to
819+
* total_heap_blks after the table scan phase, this parameter
820+
* is manually updated to the correct value when the table
821+
* scan finishes.
822+
*/
823+
pgstat_progress_update_param(PROGRESS_CLUSTER_HEAP_BLKS_SCANNED,
824+
heapScan->rs_nblocks);
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break;
826+
}
814827

815828
/*
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* In scan-and-sort mode and also VACUUM FULL, set heap blocks
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* scanned
831+
*
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* Note that heapScan may start at an offset and wrap around, i.e.
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* rs_startblock may be >0, and rs_cblock may end with a number
834+
* below rs_startblock. To prevent showing this wraparound to the
835+
* user, we offset rs_cblock by rs_startblock (modulo rs_nblocks).
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*/
819-
pgstat_progress_update_param(PROGRESS_CLUSTER_HEAP_BLKS_SCANNED,
820-
heapScan->rs_cblock+1);
837+
if (prev_cblock!=heapScan->rs_cblock)
838+
{
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pgstat_progress_update_param(PROGRESS_CLUSTER_HEAP_BLKS_SCANNED,
840+
(heapScan->rs_cblock+
841+
heapScan->rs_nblocks-
842+
heapScan->rs_startblock
843+
) %heapScan->rs_nblocks+1);
844+
prev_cblock=heapScan->rs_cblock;
845+
}
821846
}
822847

823848
tuple=ExecFetchSlotHeapTuple(slot, false,NULL);

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