database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-31 22:04:40 +03:00
Code Activity

Fix dynahash's HASH_FIXED_SIZE ("isfixed") option.

Browse Source 
This flag was effectively a no-op in EXEC_BACKEND (ie, Windows)
builds, because it was kept in the process-local HTAB struct,
and it could only ever become set in the postmaster's copy.

The simplest fix is to move it to the shared HASHHDR struct.
We could keep a copy in HTAB as well, as we do with keysize
and some other fields, but the "too much contention" argument
doesn't seem to apply here: we only examine isfixed during
element_alloc(), which had better not get hit very often for
a shared hashtable.

This oversight dates to 7c797e719 which invented the option.
But back-patching doesn't seem appropriate given the lack of
field complaints.  If there is anyone running an affected
workload on Windows, they might be unhappy about the behavior
changing in a minor release.

Author: Aidar Imamov <a.imamov@postgrespro.ru>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/4d0cb35ff01c5c74d2b9a582ecb73823@postgrespro.ru
This commit is contained in:
Tom Lane
2025-07-25 10:56:55 -04:00
parent 1dfe3ef3f9
commit 5457ea46d1
1 changed files with 7 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
src/backend/utils/hash/dynahash.c
View File

@ -195,6 +195,7 @@ struct HASHHDR
long ssize; /* segment size --- must be power of 2 */
int sshift; /* segment shift = log2(ssize) */
int nelem_alloc; /* number of entries to allocate at once */
bool isfixed; /* if true, don't enlarge */
#ifdef HASH_STATISTICS
@ -227,7 +228,6 @@ struct HTAB
MemoryContext hcxt; /* memory context if default allocator used */
char *tabname; /* table name (for error messages) */
bool isshared; /* true if table is in shared memory */
bool isfixed; /* if true, don't enlarge */
/* freezing a shared table isn't allowed, so we can keep state here */
bool frozen; /* true = no more inserts allowed */
@ -618,8 +618,10 @@ hash_create(const char *tabname, long nelem, const HASHCTL *info, int flags)
}
}
/* Set isfixed if requested, but not till after we build initial entries */
if (flags & HASH_FIXED_SIZE)
hashp->isfixed = true;
hctl->isfixed = true;
return hashp;
}
@ -644,6 +646,8 @@ hdefault(HTAB *hashp)
hctl->ssize = DEF_SEGSIZE;
hctl->sshift = DEF_SEGSIZE_SHIFT;
hctl->isfixed = false; /* can be enlarged */
#ifdef HASH_STATISTICS
hctl->accesses = hctl->collisions = 0;
#endif
@ -1713,7 +1717,7 @@ element_alloc(HTAB *hashp, int nelem, int freelist_idx)
HASHELEMENT *prevElement;
int i;
if (hashp->isfixed)
if (hctl->isfixed)
return false;
/* Each element has a HASHELEMENT header plus user data. */