From 5457ea46d181f8b8dbe1ae482720b23bff4029de Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 25 Jul 2025 10:56:55 -0400 Subject: [PATCH] Fix dynahash's HASH_FIXED_SIZE ("isfixed") option. 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 Reviewed-by: Tom Lane Discussion: https://postgr.es/m/4d0cb35ff01c5c74d2b9a582ecb73823@postgrespro.ru --- src/backend/utils/hash/dynahash.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/src/backend/utils/hash/dynahash.c b/src/backend/utils/hash/dynahash.c index 1ad155d446e..42e9be274fc 100644 --- a/src/backend/utils/hash/dynahash.c +++ b/src/backend/utils/hash/dynahash.c @@ -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. */ -- 2.47.2