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Fix hash size estimation compatbility for PG11 and below.

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Thanks to github user nikhil-postgres for the report.

While at it also fix a thinko in the size estimation which lead to greatly
overestimated hypothetical hash index sizes.
This commit is contained in:
Julien Rouhaud 2021-03-24 16:27:40 +08:00
parent c93081f35e
commit a4acac04d1
2 changed files with 18 additions and 3 deletions
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1
CONTRIBUTORS.md
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@ -16,3 +16,4 @@ People who contributed to hypopg:
* Extortioner01
* nagaraju11
* ibrahim edib kokdemir
* github user nikhil-postgres

20
hypopg_index.c
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@ -57,6 +57,9 @@
#endif
#include "parser/parse_utilcmd.h"
#include "parser/parser.h"
#if PG_VERSION_NUM >= 120000
#include "port/pg_bitutils.h"
#endif
#include "storage/bufmgr.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
@ -1907,6 +1910,7 @@ hypo_estimate_index(hypoIndex * entry, RelOptInfo *rel)
uint32 num_buckets;
uint32 num_overflow;
uint32 num_bitmap;
uint32 lshift;
/*
* Determine the target fill factor (in tuples per bucket) for this index.
@ -1947,12 +1951,22 @@ hypo_estimate_index(hypoIndex * entry, RelOptInfo *rel)
num_overflow = Max(0, ((entry->tuples - (num_buckets * ffactor)) /
ffactor) + 1);
/* find largest bitmap array size that will fit in page size */
#if PG_VERSION_NUM >= 120000
lshift = pg_leftmost_one_pos32(HypoHashGetMaxBitmapSize());
#else
for (lshift = _hash_log2(HypoHashGetMaxBitmapSize()); lshift > 0; --lshift)
{
if ((1 << lshift) <= HypoHashGetMaxBitmapSize())
break;
}
#endif
/*
* Naive estimate of bitmap pages, using the previously computed number of
* Naive estimate of bitmap pages, using the previously computed number of
* overflow pages.
*/
num_bitmap = Max(1, num_overflow /
pg_leftmost_one_pos32(HypoHashGetMaxBitmapSize()));
num_bitmap = Max(1, num_overflow / (1 <<lshift));
/* Simply add all computed pages, plus one extra block for the meta page */
entry->pages = num_buckets + num_overflow + num_bitmap + 1;