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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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25
src/backend/storage/file/reinit.c
View File

@@ -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);