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Fix bug in hashbulkdelete.

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Commit 6d46f4783efe457f74816a75173eb23ed8930020 failed to account for
the possibility that hashbulkdelete() might encounter a bucket that
has been split since it began scanning the bucket array.  Repair.

Extracted from a larger pathc by Amit Kapila; I rewrote the comment.
This commit is contained in:
Robert Haas 2016-12-13 12:16:02 -05:00
parent a25665088d
commit 501c7b94bc
1 changed files with 19 additions and 3 deletions
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22
src/backend/access/hash/hash.c
View File

@ -523,7 +523,8 @@ hashbulkdelete(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
orig_maxbucket = metap->hashm_maxbucket;
orig_ntuples = metap->hashm_ntuples;
memcpy(&local_metapage, metap, sizeof(local_metapage));
_hash_relbuf(rel, metabuf);
/* release the lock, but keep pin */
_hash_chgbufaccess(rel, metabuf, HASH_READ, HASH_NOLOCK);
/* Scan the buckets that we know exist */
cur_bucket = 0;
@ -563,8 +564,23 @@ loop_top:
*/
if (!H_BUCKET_BEING_SPLIT(bucket_opaque) &&
H_NEEDS_SPLIT_CLEANUP(bucket_opaque))
{
split_cleanup = true;
/*
* This bucket might have been split since we last held a lock on
* the metapage. If so, hashm_maxbucket, hashm_highmask and
* hashm_lowmask might be old enough to cause us to fail to remove
* tuples left behind by the most recent split. To prevent that,
* now that the primary page of the target bucket has been locked
* (and thus can't be further split), update our cached metapage
* data.
*/
_hash_chgbufaccess(rel, metabuf, HASH_NOLOCK, HASH_READ);
memcpy(&local_metapage, metap, sizeof(local_metapage));
_hash_chgbufaccess(rel, metabuf, HASH_READ, HASH_NOLOCK);
}
bucket_buf = buf;
hashbucketcleanup(rel, cur_bucket, bucket_buf, blkno, info->strategy,
@ -581,7 +597,7 @@ loop_top:
}
/* Write-lock metapage and check for split since we started */
metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_WRITE, LH_META_PAGE);
_hash_chgbufaccess(rel, metabuf, HASH_NOLOCK, HASH_WRITE);
metap = HashPageGetMeta(BufferGetPage(metabuf));
if (cur_maxbucket != metap->hashm_maxbucket)
@ -589,7 +605,7 @@ loop_top:
/* There's been a split, so process the additional bucket(s) */
cur_maxbucket = metap->hashm_maxbucket;
memcpy(&local_metapage, metap, sizeof(local_metapage));
_hash_relbuf(rel, metabuf);
_hash_chgbufaccess(rel, metabuf, HASH_READ, HASH_NOLOCK);
goto loop_top;
}