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, 1 insertions, 3 deletions

diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
index 4b18be5b272..89087a7be31 100644
--- a/src/backend/commands/prepare.c
+++ b/src/backend/commands/prepare.c
@@ -406,15 +406,13 @@ InitQueryHashTable(void)
 {
 	HASHCTL		hash_ctl;
 
-	MemSet(&hash_ctl, 0, sizeof(hash_ctl));
-
 	hash_ctl.keysize = NAMEDATALEN;
 	hash_ctl.entrysize = sizeof(PreparedStatement);
 
 	prepared_queries = hash_create("Prepared Queries",
 								   32,
 								   &hash_ctl,
-								   HASH_ELEM);
+								   HASH_ELEM | HASH_STRINGS);
 }
 
 /*