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/590625.1607878171@sss.pgh.pa.us

1 files changed, 10 insertions, 15 deletions

diff --git a/src/backend/storage/file/reinit.c b/src/backend/storage/file/reinit.c
index 0c2094f7663..8700f7f19a4 100644
--- a/src/backend/storage/file/reinit.c
+++ b/src/backend/storage/file/reinit.c
@@ -30,7 +30,7 @@ static void ResetUnloggedRelationsInDbspaceDir(const char *dbspacedirname,
 
 typedef struct
 {
-	char		oid[OIDCHARS + 1];
+	Oid			reloid;			/* hash key */
 } unlogged_relation_entry;
 
 /*
@@ -172,10 +172,11 @@ ResetUnloggedRelationsInDbspaceDir(const char *dbspacedirname, int op)
 		 * need to be reset.  Otherwise, this cleanup operation would be
 		 * O(n^2).
 		 */
-		memset(&ctl, 0, sizeof(ctl));
-		ctl.keysize = sizeof(unlogged_relation_entry);
+		ctl.keysize = sizeof(Oid);
 		ctl.entrysize = sizeof(unlogged_relation_entry);
-		hash = hash_create("unlogged hash", 32, &ctl, HASH_ELEM);
+		ctl.hcxt = CurrentMemoryContext;
+		hash = hash_create("unlogged relation OIDs", 32, &ctl,
+						   HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
 
 		/* Scan the directory. */
 		dbspace_dir = AllocateDir(dbspacedirname);
@@ -198,9 +199,8 @@ ResetUnloggedRelationsInDbspaceDir(const char *dbspacedirname, int op)
 			 * Put the OID portion of the name into the hash table, if it
 			 * isn't already.
 			 */
-			memset(ent.oid, 0, sizeof(ent.oid));
-			memcpy(ent.oid, de->d_name, oidchars);
-			hash_search(hash, &ent, HASH_ENTER, NULL);
+			ent.reloid = atooid(de->d_name);
+			(void) hash_search(hash, &ent, HASH_ENTER, NULL);
 		}
 
 		/* Done with the first pass. */
@@ -224,7 +224,6 @@ ResetUnloggedRelationsInDbspaceDir(const char *dbspacedirname, int op)
 		{
 			ForkNumber	forkNum;
 			int			oidchars;
-			bool		found;
 			unlogged_relation_entry ent;
 
 			/* Skip anything that doesn't look like a relation data file. */
@@ -238,14 +237,10 @@ ResetUnloggedRelationsInDbspaceDir(const char *dbspacedirname, int op)
 
 			/*
 			 * See whether the OID portion of the name shows up in the hash
-			 * table.
+			 * table.  If so, nuke it!
 			 */
-			memset(ent.oid, 0, sizeof(ent.oid));
-			memcpy(ent.oid, de->d_name, oidchars);
-			hash_search(hash, &ent, HASH_FIND, &found);
-
-			/* If so, nuke it! */
-			if (found)
+			ent.reloid = atooid(de->d_name);
+			if (hash_search(hash, &ent, HASH_FIND, NULL))
 			{
 				snprintf(rm_path, sizeof(rm_path), "%s/%s",
 						 dbspacedirname, de->d_name);