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Improve hash_create()'s API for some added robustness.

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Invent a new flag bit HASH_STRINGS to specify C-string hashing, which
was formerly the default; and add assertions insisting that exactly
one of the bits HASH_STRINGS, HASH_BLOBS, and HASH_FUNCTION be set.
This is in hopes of preventing recurrences of the type of oversight
fixed in commit a1b8aa1e4 (i.e., mistakenly omitting HASH_BLOBS).

Also, when HASH_STRINGS is specified, insist that the keysize be
more than 8 bytes.  This is a heuristic, but it should catch
accidental use of HASH_STRINGS for integer or pointer keys.
(Nearly all existing use-cases set the keysize to NAMEDATALEN or
more, so there's little reason to think this restriction should
be problematic.)

Tweak hash_create() to insist that the HASH_ELEM flag be set, and
remove the defaults it had for keysize and entrysize.  Since those
defaults were undocumented and basically useless, no callers
omitted HASH_ELEM anyway.

Also, remove memset's zeroing the HASHCTL parameter struct from
those callers that had one.  This has never been really necessary,
and while it wasn't a bad coding convention it was confusing that
some callers did it and some did not.  We might as well save a few
cycles by standardizing on "not".

Also improve the documentation for hash_create().

In passing, improve reinit.c's usage of a hash table by storing
the key as a binary Oid rather than a string; and, since that's
a temporary hash table, allocate it in CurrentMemoryContext for
neatness.

Discussion: https://postgr.es/m/590625.1607878171@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2020-12-15 11:38:53 -05:00
parent a58db3aa10
commit b3817f5f77
63 changed files with 112 additions and 158 deletions
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1
src/backend/storage/lmgr/lock.c
View File

@@ -419,7 +419,6 @@ InitLocks(void)
* Allocate hash table for LOCK structs. This stores per-locked-object
* information.
*/
MemSet(&info, 0, sizeof(info));
info.keysize = sizeof(LOCKTAG);
info.entrysize = sizeof(LOCK);
info.num_partitions = NUM_LOCK_PARTITIONS;

1
src/backend/storage/lmgr/lwlock.c
View File

@@ -342,7 +342,6 @@ init_lwlock_stats(void)
ALLOCSET_DEFAULT_SIZES);
MemoryContextAllowInCriticalSection(lwlock_stats_cxt, true);
MemSet(&ctl, 0, sizeof(ctl));
ctl.keysize = sizeof(lwlock_stats_key);
ctl.entrysize = sizeof(lwlock_stats);
ctl.hcxt = lwlock_stats_cxt;

4
src/backend/storage/lmgr/predicate.c
View File

@@ -1096,7 +1096,6 @@ InitPredicateLocks(void)
* Allocate hash table for PREDICATELOCKTARGET structs. This stores
* per-predicate-lock-target information.
*/
MemSet(&info, 0, sizeof(info));
info.keysize = sizeof(PREDICATELOCKTARGETTAG);
info.entrysize = sizeof(PREDICATELOCKTARGET);
info.num_partitions = NUM_PREDICATELOCK_PARTITIONS;
@@ -1129,7 +1128,6 @@ InitPredicateLocks(void)
* Allocate hash table for PREDICATELOCK structs. This stores per
* xact-lock-of-a-target information.
*/
MemSet(&info, 0, sizeof(info));
info.keysize = sizeof(PREDICATELOCKTAG);
info.entrysize = sizeof(PREDICATELOCK);
info.hash = predicatelock_hash;
@@ -1212,7 +1210,6 @@ InitPredicateLocks(void)
* Allocate hash table for SERIALIZABLEXID structs. This stores per-xid
* information for serializable transactions which have accessed data.
*/
MemSet(&info, 0, sizeof(info));
info.keysize = sizeof(SERIALIZABLEXIDTAG);
info.entrysize = sizeof(SERIALIZABLEXID);
@@ -1853,7 +1850,6 @@ CreateLocalPredicateLockHash(void)
/* Initialize the backend-local hash table of parent locks */
Assert(LocalPredicateLockHash == NULL);
MemSet(&hash_ctl, 0, sizeof(hash_ctl));
hash_ctl.keysize = sizeof(PREDICATELOCKTARGETTAG);
hash_ctl.entrysize = sizeof(LOCALPREDICATELOCK);
LocalPredicateLockHash = hash_create("Local predicate lock",