Hello, Robert
> Basically, the burden for you to impose a new coding rule on everybody
> who uses shared hash tables in the future is very high.
I fixed an issue you described. Number of spinlocks doesn't depend of
NUM_LOCK_PARTITIONS anymore and could be specified for each hash table
on a calling side.
I did a benchmark described in a first message of this thread again.
Currently I don't have access to the same 60-core server so I used more
common 12-core server (24 with HT). According to this benchmark TPS
increment depends on NUM_LOCK_PARTITIONS and default number of
spinlocks this way:
pgbench -f pgbench.sql -T 150 -P 1 -c 40 -j 12
DMN | NLP = 16 | NLP = 32 | NLP = 64 | NLP = 128
-----|----------|----------|----------|----------
8 | +15.1% | +28.2% | +34.1% | +33.7%
16 | +16.6% | +30.9% | +37.0% | +40.8%
32 | +15.1% | +33.9% | +39.5% | +41.9%
64 | +15.0% | +31.9% | +40.1% | +42.9%
128 | +7.7% | +24.7% | +29.6% | +31.6%
* NLP = NUM_LOCK_PARTITIONS
* DMN = DEFAULT_MUTEXES_NUM
I realize this benchmark doesn't represent any possible workload so for
attached patch I choose NUM_LOCK_PARTITIONS = DEFAULT_MUTEXES_NUM = 32.
It seems to be a reasonable compromise of a speedup according to
"synthetic and meaningless in practice" benchmark and number of used
locks which could mean quite a lot in practice. Still this values could
be easily changed in any moment.
Here are before/after benchmark results for this concrete patch.
BEFORE
pgbench (default):
tps = 1295.798531 (including connections establishing)
tps = 1295.858295 (excluding connections establishing)
pgbench -f pgbench.sql:
tps = 1020.072172 (including connections establishing)
tps = 1020.116888 (excluding connections establishing)
AFTER
pgbench (default):
tps = 1299.369807 (including connections establishing)
tps = 1299.429764 (excluding connections establishing)
pgbench -f pgbench.sql:
tps = 1365.749333 (including connections establishing)
tps = 1365.814384 (excluding connections establishing)
So as I understand this patch solves a lock contention problem and
doesn't make anything else worse.
diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index dffc477..9a15a2a 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -495,7 +495,7 @@ pgss_shmem_startup(void)
info.hash = pgss_hash_fn;
info.match = pgss_match_fn;
pgss_hash = ShmemInitHash("pg_stat_statements hash",
- pgss_max, pgss_max,
+ pgss_max,
&info,
HASH_ELEM | HASH_FUNCTION | HASH_COMPARE);
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index 39e8baf..dd5acb7 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -62,7 +62,7 @@ InitBufTable(int size)
info.num_partitions = NUM_BUFFER_PARTITIONS;
SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
- size, size,
+ size,
&info,
HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
}
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index 81506ea..4c18701 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -237,7 +237,7 @@ InitShmemIndex(void)
hash_flags = HASH_ELEM;
ShmemIndex = ShmemInitHash("ShmemIndex",
- SHMEM_INDEX_SIZE, SHMEM_INDEX_SIZE,
+ SHMEM_INDEX_SIZE,
&info, hash_flags);
}
@@ -255,17 +255,12 @@ InitShmemIndex(void)
* exceeded substantially (since it's used to compute directory size and
* the hash table buckets will get overfull).
*
- * init_size is the number of hashtable entries to preallocate. For a table
- * whose maximum size is certain, this should be equal to max_size; that
- * ensures that no run-time out-of-shared-memory failures can occur.
- *
* Note: before Postgres 9.0, this function returned NULL for some failure
* cases. Now, it always throws error instead, so callers need not check
* for NULL.
*/
HTAB *
ShmemInitHash(const char *name, /* table string name for shmem index */
- long init_size, /* initial table size */
long max_size, /* max size of the table */
HASHCTL *infoP, /* info about key and bucket size */
int hash_flags) /* info about infoP */
@@ -299,7 +294,7 @@ ShmemInitHash(const char *name, /* table string name for shmem index */
/* Pass location of hashtable header to hash_create */
infoP->hctl = (HASHHDR *) location;
- return hash_create(name, init_size, infoP, hash_flags);
+ return hash_create(name, max_size, infoP, hash_flags);
}
/*
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
index e3e9599..fc20a67 100644
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -374,18 +374,10 @@ void
InitLocks(void)
{
HASHCTL info;
- long init_table_size,
- max_table_size;
+ long max_table_size;
bool found;
/*
- * Compute init/max size to request for lock hashtables. Note these
- * calculations must agree with LockShmemSize!
- */
- max_table_size = NLOCKENTS();
- init_table_size = max_table_size / 2;
-
- /*
* Allocate hash table for LOCK structs. This stores per-locked-object
* information.
*/
@@ -393,16 +385,15 @@ InitLocks(void)
info.keysize = sizeof(LOCKTAG);
info.entrysize = sizeof(LOCK);
info.num_partitions = NUM_LOCK_PARTITIONS;
+ max_table_size = NLOCKENTS();
LockMethodLockHash = ShmemInitHash("LOCK hash",
- init_table_size,
max_table_size,
&info,
HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
/* Assume an average of 2 holders per lock */
max_table_size *= 2;
- init_table_size *= 2;
/*
* Allocate hash table for PROCLOCK structs. This stores
@@ -414,7 +405,6 @@ InitLocks(void)
info.num_partitions = NUM_LOCK_PARTITIONS;
LockMethodProcLockHash = ShmemInitHash("PROCLOCK hash",
- init_table_size,
max_table_size,
&info,
HASH_ELEM | HASH_FUNCTION | HASH_PARTITION);
diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c
index 026d2b9..be73a60 100644
--- a/src/backend/storage/lmgr/predicate.c
+++ b/src/backend/storage/lmgr/predicate.c
@@ -1117,7 +1117,6 @@ InitPredicateLocks(void)
PredicateLockTargetHash = ShmemInitHash("PREDICATELOCKTARGET hash",
max_table_size,
- max_table_size,
&info,
HASH_ELEM | HASH_BLOBS |
HASH_PARTITION | HASH_FIXED_SIZE);
@@ -1145,7 +1144,6 @@ InitPredicateLocks(void)
PredicateLockHash = ShmemInitHash("PREDICATELOCK hash",
max_table_size,
- max_table_size,
&info,
HASH_ELEM | HASH_FUNCTION |
HASH_PARTITION | HASH_FIXED_SIZE);
@@ -1226,7 +1224,6 @@ InitPredicateLocks(void)
SerializableXidHash = ShmemInitHash("SERIALIZABLEXID hash",
max_table_size,
- max_table_size,
&info,
HASH_ELEM | HASH_BLOBS |
HASH_FIXED_SIZE);
diff --git a/src/backend/utils/hash/dynahash.c b/src/backend/utils/hash/dynahash.c
index 24a53da..6a49958 100644
--- a/src/backend/utils/hash/dynahash.c
+++ b/src/backend/utils/hash/dynahash.c
@@ -15,7 +15,7 @@
* to hash_create. This prevents any attempt to split buckets on-the-fly.
* Therefore, each hash bucket chain operates independently, and no fields
* of the hash header change after init except nentries and freeList.
- * A partitioned table uses a spinlock to guard changes of those two fields.
+ * A partitioned table uses spinlocks to guard changes of those fields.
* This lets any subset of the hash buckets be treated as a separately
* lockable partition. We expect callers to use the low-order bits of a
* lookup key's hash value as a partition number --- this will work because
@@ -111,6 +111,12 @@
#define DEF_DIRSIZE 256
#define DEF_FFACTOR 1 /* default fill factor */
+/*
+ * Default and maximum number of mutexes and respectively number of nentries
+ * and freeLists (see below). Both values should be power of 2.
+ */
+#define DEFAULT_MUTEXES_NUM 32
+#define MAX_MUTEXES_NUM 128
/* A hash bucket is a linked list of HASHELEMENTs */
typedef HASHELEMENT *HASHBUCKET;
@@ -128,12 +134,24 @@ typedef HASHBUCKET *HASHSEGMENT;
*/
struct HASHHDR
{
- /* In a partitioned table, take this lock to touch nentries or freeList */
- slock_t mutex; /* unused if not partitioned table */
-
- /* These fields change during entry addition/deletion */
- long nentries; /* number of entries in hash table */
- HASHELEMENT *freeList; /* linked list of free elements */
+ /*
+ * There are two fields declared below: nentries and freeList. nentries
+ * stores current number of entries in a hash table. freeList is a linked
+ * list of free elements.
+ *
+ * To keep these fields consistent in a partitioned table we need to
+ * synchronize access to them using a spinlock. But it turned out that a
+ * single spinlock can create a bottleneck. To prevent lock contention an
+ * array of num_mutexes spinlocks is used, where num_mutexes should be
+ * power of two less or equal to MAX_MUTEXES_NUM. Each spinlock protects
+ * one element of nentries and freeList arrays.
+ *
+ * If hash table is not partitioned only nentries[0] and freeList[0] are
+ * used and spinlocks are not used at all.
+ */
+ slock_t mutex[MAX_MUTEXES_NUM]; /* array of spinlocks */
+ long nentries[MAX_MUTEXES_NUM]; /* number of entries */
+ HASHELEMENT *freeList[MAX_MUTEXES_NUM]; /* lists of free elements */
/* These fields can change, but not in a partitioned table */
/* Also, dsize can't change in a shared table, even if unpartitioned */
@@ -147,6 +165,8 @@ struct HASHHDR
Size keysize; /* hash key length in bytes */
Size entrysize; /* total user element size in bytes */
long num_partitions; /* # partitions (must be power of 2), or 0 */
+ long num_mutexes; /* # mutexes (must be power of 2) */
+ long mutexes_mask; /* equals num_mutexes - 1 */
long ffactor; /* target fill factor */
long max_dsize; /* 'dsize' limit if directory is fixed size */
long ssize; /* segment size --- must be power of 2 */
@@ -166,6 +186,8 @@ struct HASHHDR
#define IS_PARTITIONED(hctl) ((hctl)->num_partitions != 0)
+#define FREELIST_IDX(hctl, hashcode) (IS_PARTITIONED(hctl) ? hashcode & hctl->mutexes_mask : 0)
+
/*
* Top control structure for a hashtable --- in a shared table, each backend
* has its own copy (OK since no fields change at runtime)
@@ -219,10 +241,10 @@ static long hash_accesses,
*/
static void *DynaHashAlloc(Size size);
static HASHSEGMENT seg_alloc(HTAB *hashp);
-static bool element_alloc(HTAB *hashp, int nelem);
+static bool element_alloc(HTAB *hashp, int nelem, int freelist_idx);
static bool dir_realloc(HTAB *hashp);
static bool expand_table(HTAB *hashp);
-static HASHBUCKET get_hash_entry(HTAB *hashp);
+static HASHBUCKET get_hash_entry(HTAB *hashp, int freelist_idx);
static void hdefault(HTAB *hashp);
static int choose_nelem_alloc(Size entrysize);
static bool init_htab(HTAB *hashp, long nelem);
@@ -282,6 +304,10 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
{
HTAB *hashp;
HASHHDR *hctl;
+ int i,
+ partitions_number,
+ nelem_alloc,
+ nelem_alloc_first;
/*
* For shared hash tables, we have a local hash header (HTAB struct) that
@@ -417,6 +443,24 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
hctl = hashp->hctl;
+ /*
+ * Set num_mutexes and mutexes_mask
+ */
+ if (flags & HASH_NMUTEXES)
+ {
+ hctl->num_mutexes = next_pow2_int(info->num_mutexes);
+
+ if (hctl->num_mutexes > MAX_MUTEXES_NUM)
+ hctl->num_mutexes = MAX_MUTEXES_NUM;
+ }
+ else
+ hctl->num_mutexes = DEFAULT_MUTEXES_NUM;
+
+ Assert(hctl->num_mutexes == next_pow2_int(hctl->num_mutexes));
+
+ hctl->mutexes_mask = hctl->num_mutexes - 1;
+
+
if (flags & HASH_PARTITION)
{
/* Doesn't make sense to partition a local hash table */
@@ -482,10 +526,34 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
if ((flags & HASH_SHARED_MEM) ||
nelem < hctl->nelem_alloc)
{
- if (!element_alloc(hashp, (int) nelem))
- ereport(ERROR,
- (errcode(ERRCODE_OUT_OF_MEMORY),
- errmsg("out of memory")));
+ /*
+ * If hash table is partitioned all freeLists have equal number of
+ * elements. Otherwise only freeList[0] is used.
+ */
+ if (IS_PARTITIONED(hashp->hctl))
+ partitions_number = hctl->num_mutexes;
+ else
+ partitions_number = 1;
+
+ nelem_alloc = nelem / partitions_number;
+ if (nelem_alloc == 0)
+ nelem_alloc = 1;
+
+ if (nelem_alloc * partitions_number < nelem)
+ /* Make sure all memory will be used */
+ nelem_alloc_first = nelem - nelem_alloc * (partitions_number - 1);
+ else
+ nelem_alloc_first = nelem_alloc;
+
+ for (i = 0; i < partitions_number; i++)
+ {
+ int temp = (i == 0) ? nelem_alloc_first : nelem_alloc;
+
+ if (!element_alloc(hashp, temp, i))
+ ereport(ERROR,
+ (errcode(ERRCODE_OUT_OF_MEMORY),
+ errmsg("out of memory")));
+ }
}
if (flags & HASH_FIXED_SIZE)
@@ -503,9 +571,6 @@ hdefault(HTAB *hashp)
MemSet(hctl, 0, sizeof(HASHHDR));
- hctl->nentries = 0;
- hctl->freeList = NULL;
-
hctl->dsize = DEF_DIRSIZE;
hctl->nsegs = 0;
@@ -572,12 +637,14 @@ init_htab(HTAB *hashp, long nelem)
HASHSEGMENT *segp;
int nbuckets;
int nsegs;
+ int i;
/*
* initialize mutex if it's a partitioned table
*/
if (IS_PARTITIONED(hctl))
- SpinLockInit(&hctl->mutex);
+ for (i = 0; i < hctl->num_mutexes; i++)
+ SpinLockInit(&(hctl->mutex[i]));
/*
* Divide number of elements by the fill factor to determine a desired
@@ -648,7 +715,7 @@ init_htab(HTAB *hashp, long nelem)
"HIGH MASK ", hctl->high_mask,
"LOW MASK ", hctl->low_mask,
"NSEGS ", hctl->nsegs,
- "NENTRIES ", hctl->nentries);
+ "NENTRIES ", hash_get_num_entries(hctl));
#endif
return true;
}
@@ -769,7 +836,7 @@ hash_stats(const char *where, HTAB *hashp)
where, hashp->hctl->accesses, hashp->hctl->collisions);
fprintf(stderr, "hash_stats: entries %ld keysize %ld maxp %u segmentcount %ld\n",
- hashp->hctl->nentries, (long) hashp->hctl->keysize,
+ hash_get_num_entries(hashp), (long) hashp->hctl->keysize,
hashp->hctl->max_bucket, hashp->hctl->nsegs);
fprintf(stderr, "%s: total accesses %ld total collisions %ld\n",
where, hash_accesses, hash_collisions);
@@ -863,6 +930,7 @@ hash_search_with_hash_value(HTAB *hashp,
HASHBUCKET currBucket;
HASHBUCKET *prevBucketPtr;
HashCompareFunc match;
+ int freelist_idx = FREELIST_IDX(hctl, hashvalue);
#if HASH_STATISTICS
hash_accesses++;
@@ -885,7 +953,7 @@ hash_search_with_hash_value(HTAB *hashp,
* order of these tests is to try to check cheaper conditions first.
*/
if (!IS_PARTITIONED(hctl) && !hashp->frozen &&
- hctl->nentries / (long) (hctl->max_bucket + 1) >= hctl->ffactor &&
+ hctl->nentries[0] / (long) (hctl->max_bucket + 1) >= hctl->ffactor &&
!has_seq_scans(hashp))
(void) expand_table(hashp);
}
@@ -943,20 +1011,20 @@ hash_search_with_hash_value(HTAB *hashp,
{
/* if partitioned, must lock to touch nentries and freeList */
if (IS_PARTITIONED(hctl))
- SpinLockAcquire(&hctl->mutex);
+ SpinLockAcquire(&(hctl->mutex[freelist_idx]));
- Assert(hctl->nentries > 0);
- hctl->nentries--;
+ Assert(hctl->nentries[freelist_idx] > 0);
+ hctl->nentries[freelist_idx]--;
/* remove record from hash bucket's chain. */
*prevBucketPtr = currBucket->link;
/* add the record to the freelist for this table. */
- currBucket->link = hctl->freeList;
- hctl->freeList = currBucket;
+ currBucket->link = hctl->freeList[freelist_idx];
+ hctl->freeList[freelist_idx] = currBucket;
if (IS_PARTITIONED(hctl))
- SpinLockRelease(&hctl->mutex);
+ SpinLockRelease(&hctl->mutex[freelist_idx]);
/*
* better hope the caller is synchronizing access to this
@@ -982,7 +1050,7 @@ hash_search_with_hash_value(HTAB *hashp,
elog(ERROR, "cannot insert into frozen hashtable \"%s\"",
hashp->tabname);
- currBucket = get_hash_entry(hashp);
+ currBucket = get_hash_entry(hashp, freelist_idx);
if (currBucket == NULL)
{
/* out of memory */
@@ -1175,41 +1243,70 @@ hash_update_hash_key(HTAB *hashp,
* create a new entry if possible
*/
static HASHBUCKET
-get_hash_entry(HTAB *hashp)
+get_hash_entry(HTAB *hashp, int freelist_idx)
{
- HASHHDR *hctl = hashp->hctl;
+ HASHHDR *hctl = hashp->hctl;
HASHBUCKET newElement;
+ int borrow_from_idx;
for (;;)
{
/* if partitioned, must lock to touch nentries and freeList */
if (IS_PARTITIONED(hctl))
- SpinLockAcquire(&hctl->mutex);
+ SpinLockAcquire(&hctl->mutex[freelist_idx]);
/* try to get an entry from the freelist */
- newElement = hctl->freeList;
+ newElement = hctl->freeList[freelist_idx];
+
if (newElement != NULL)
- break;
+ {
+ /* remove entry from freelist, bump nentries */
+ hctl->freeList[freelist_idx] = newElement->link;
+ hctl->nentries[freelist_idx]++;
+ if (IS_PARTITIONED(hctl))
+ SpinLockRelease(&hctl->mutex[freelist_idx]);
+
+ return newElement;
+ }
- /* no free elements. allocate another chunk of buckets */
if (IS_PARTITIONED(hctl))
- SpinLockRelease(&hctl->mutex);
+ SpinLockRelease(&hctl->mutex[freelist_idx]);
- if (!element_alloc(hashp, hctl->nelem_alloc))
+ /* no free elements. allocate another chunk of buckets */
+ if (!element_alloc(hashp, hctl->nelem_alloc, freelist_idx))
{
- /* out of memory */
- return NULL;
- }
- }
+ if (!IS_PARTITIONED(hctl))
+ return NULL; /* out of memory */
- /* remove entry from freelist, bump nentries */
- hctl->freeList = newElement->link;
- hctl->nentries++;
+ /* try to borrow element from another partition */
+ borrow_from_idx = freelist_idx;
+ for (;;)
+ {
+ borrow_from_idx = (borrow_from_idx + 1) & hctl->mutexes_mask;
+ if (borrow_from_idx == freelist_idx)
+ break;
- if (IS_PARTITIONED(hctl))
- SpinLockRelease(&hctl->mutex);
+ SpinLockAcquire(&(hctl->mutex[borrow_from_idx]));
+ newElement = hctl->freeList[borrow_from_idx];
+
+ if (newElement != NULL)
+ {
+ hctl->freeList[borrow_from_idx] = newElement->link;
+ SpinLockRelease(&(hctl->mutex[borrow_from_idx]));
+
+ SpinLockAcquire(&hctl->mutex[freelist_idx]);
+ hctl->nentries[freelist_idx]++;
+ SpinLockRelease(&hctl->mutex[freelist_idx]);
+
+ break;
+ }
- return newElement;
+ SpinLockRelease(&(hctl->mutex[borrow_from_idx]));
+ }
+
+ return newElement;
+ }
+ }
}
/*
@@ -1218,11 +1315,21 @@ get_hash_entry(HTAB *hashp)
long
hash_get_num_entries(HTAB *hashp)
{
+ int i;
+ long sum = hashp->hctl->nentries[0];
+
/*
* We currently don't bother with the mutex; it's only sensible to call
* this function if you've got lock on all partitions of the table.
*/
- return hashp->hctl->nentries;
+
+ if (!IS_PARTITIONED(hashp->hctl))
+ return sum;
+
+ for (i = 1; i < hashp->hctl->num_mutexes; i++)
+ sum += hashp->hctl->nentries[i];
+
+ return sum;
}
/*
@@ -1530,9 +1637,9 @@ seg_alloc(HTAB *hashp)
* allocate some new elements and link them into the free list
*/
static bool
-element_alloc(HTAB *hashp, int nelem)
+element_alloc(HTAB *hashp, int nelem, int freelist_idx)
{
- HASHHDR *hctl = hashp->hctl;
+ HASHHDR *hctl = hashp->hctl;
Size elementSize;
HASHELEMENT *firstElement;
HASHELEMENT *tmpElement;
@@ -1563,14 +1670,14 @@ element_alloc(HTAB *hashp, int nelem)
/* if partitioned, must lock to touch freeList */
if (IS_PARTITIONED(hctl))
- SpinLockAcquire(&hctl->mutex);
+ SpinLockAcquire(&hctl->mutex[freelist_idx]);
/* freelist could be nonempty if two backends did this concurrently */
- firstElement->link = hctl->freeList;
- hctl->freeList = prevElement;
+ firstElement->link = hctl->freeList[freelist_idx];
+ hctl->freeList[freelist_idx] = prevElement;
if (IS_PARTITIONED(hctl))
- SpinLockRelease(&hctl->mutex);
+ SpinLockRelease(&hctl->mutex[freelist_idx]);
return true;
}
diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h
index 2bbe1b6..6e44027 100644
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -142,7 +142,7 @@ extern PGDLLIMPORT int NamedLWLockTrancheRequests;
#define NUM_BUFFER_PARTITIONS 128
/* Number of partitions the shared lock tables are divided into */
-#define LOG2_NUM_LOCK_PARTITIONS 4
+#define LOG2_NUM_LOCK_PARTITIONS 5
#define NUM_LOCK_PARTITIONS (1 << LOG2_NUM_LOCK_PARTITIONS)
/* Number of partitions the shared predicate lock tables are divided into */
diff --git a/src/include/storage/shmem.h b/src/include/storage/shmem.h
index 6468e66..50cf928 100644
--- a/src/include/storage/shmem.h
+++ b/src/include/storage/shmem.h
@@ -37,7 +37,7 @@ extern void InitShmemAllocation(void);
extern void *ShmemAlloc(Size size);
extern bool ShmemAddrIsValid(const void *addr);
extern void InitShmemIndex(void);
-extern HTAB *ShmemInitHash(const char *name, long init_size, long max_size,
+extern HTAB *ShmemInitHash(const char *name, long max_size,
HASHCTL *infoP, int hash_flags);
extern void *ShmemInitStruct(const char *name, Size size, bool *foundPtr);
extern Size add_size(Size s1, Size s2);
diff --git a/src/include/utils/hsearch.h b/src/include/utils/hsearch.h
index 007ba2c..8e2e6a1 100644
--- a/src/include/utils/hsearch.h
+++ b/src/include/utils/hsearch.h
@@ -69,6 +69,7 @@ typedef struct HASHCTL
long dsize; /* (initial) directory size */
long max_dsize; /* limit to dsize if dir size is limited */
long ffactor; /* fill factor */
+ long num_mutexes; /* number of mutexes */
Size keysize; /* hash key length in bytes */
Size entrysize; /* total user element size in bytes */
HashValueFunc hash; /* hash function */
@@ -94,6 +95,7 @@ typedef struct HASHCTL
#define HASH_SHARED_MEM 0x0800 /* Hashtable is in shared memory */
#define HASH_ATTACH 0x1000 /* Do not initialize hctl */
#define HASH_FIXED_SIZE 0x2000 /* Initial size is a hard limit */
+#define HASH_NMUTEXES 0x4000 /* Set number of mutexes */
/* max_dsize value to indicate expansible directory */
--
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