Oleksii Kliukin <al...@hintbits.com> writes:
>> On 30 Dec 2015, at 17:02, Tom Lane <t...@sss.pgh.pa.us> wrote:
>> Another idea would be to use the heap's row density as calculated
>> by the last ANALYZE (ie, reltuples/relpages), with a fallback to 100
>> if relpages=0. This'd only be convenient if the bitmap scan node has
>> the parent heap rel open, which it might not.
> +1
Any objections to the attached?
regards, tom lane
diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index 2622a7e..64bf788 100644
*** a/src/backend/access/brin/brin.c
--- b/src/backend/access/brin/brin.c
*************** bringetbitmap(PG_FUNCTION_ARGS)
*** 279,286 ****
Relation heapRel;
BrinOpaque *opaque;
BlockNumber nblocks;
BlockNumber heapBlk;
! int totalpages = 0;
FmgrInfo *consistentFn;
MemoryContext oldcxt;
MemoryContext perRangeCxt;
--- 279,287 ----
Relation heapRel;
BrinOpaque *opaque;
BlockNumber nblocks;
+ int heap_tuples_per_page;
BlockNumber heapBlk;
! int64 totalpages = 0;
FmgrInfo *consistentFn;
MemoryContext oldcxt;
MemoryContext perRangeCxt;
*************** bringetbitmap(PG_FUNCTION_ARGS)
*** 291,301 ****
/*
* We need to know the size of the table so that we know how long to
! * iterate on the revmap.
*/
heapOid = IndexGetRelation(RelationGetRelid(idxRel), false);
heapRel = heap_open(heapOid, AccessShareLock);
nblocks = RelationGetNumberOfBlocks(heapRel);
heap_close(heapRel, AccessShareLock);
/*
--- 292,309 ----
/*
* We need to know the size of the table so that we know how long to
! * iterate on the revmap. While we have it open, estimate the number of
! * tuples per heap page for use later.
*/
heapOid = IndexGetRelation(RelationGetRelid(idxRel), false);
heapRel = heap_open(heapOid, AccessShareLock);
nblocks = RelationGetNumberOfBlocks(heapRel);
+ if (heapRel->rd_rel->relpages != 0 && heapRel->rd_rel->reltuples > 0)
+ heap_tuples_per_page = (int)
+ ((double) heapRel->rd_rel->reltuples /
+ (BlockNumber) heapRel->rd_rel->relpages);
+ else /* if no info, assume 100-byte tuples */
+ heap_tuples_per_page = BLCKSZ / 100;
heap_close(heapRel, AccessShareLock);
/*
*************** bringetbitmap(PG_FUNCTION_ARGS)
*** 447,457 ****
ReleaseBuffer(buf);
/*
! * XXX We have an approximation of the number of *pages* that our scan
! * returns, but we don't have a precise idea of the number of heap tuples
! * involved.
*/
! PG_RETURN_INT64(totalpages * 10);
}
/*
--- 455,465 ----
ReleaseBuffer(buf);
/*
! * We have an approximation of the number of pages that our scan returns,
! * but we don't have a precise idea of the number of heap tuples involved.
! * We have to estimate based on average tuple density.
*/
! PG_RETURN_INT64(totalpages * heap_tuples_per_page);
}
/*
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