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

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/[email protected]

1 files changed, 0 insertions, 4 deletions

diff --git a/src/backend/replication/pgoutput/pgoutput.c b/src/backend/replication/pgoutput/pgoutput.c
index 9c997aed836..49d25b02d74 100644
--- a/src/backend/replication/pgoutput/pgoutput.c
+++ b/src/backend/replication/pgoutput/pgoutput.c
@@ -867,22 +867,18 @@ static void
 init_rel_sync_cache(MemoryContext cachectx)
 {
 	HASHCTL		ctl;
-	MemoryContext old_ctxt;
 
 	if (RelationSyncCache != NULL)
 		return;
 
 	/* Make a new hash table for the cache */
-	MemSet(&ctl, 0, sizeof(ctl));
 	ctl.keysize = sizeof(Oid);
 	ctl.entrysize = sizeof(RelationSyncEntry);
 	ctl.hcxt = cachectx;
 
-	old_ctxt = MemoryContextSwitchTo(cachectx);
 	RelationSyncCache = hash_create("logical replication output relation cache",
 									128, &ctl,
 									HASH_ELEM | HASH_CONTEXT | HASH_BLOBS);
-	(void) MemoryContextSwitchTo(old_ctxt);
 
 	Assert(RelationSyncCache != NULL);