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help / color / mirror / Atom feedFrom: Rahila Syed <[email protected]>
To: Tomas Vondra <[email protected]>
Cc: Nazir Bilal Yavuz <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Subject: Re: Improve monitoring of shared memory allocations
Date: Mon, 31 Mar 2025 04:31:33 +0530
Message-ID: <CAH2L28soW40DafNmLEEWMrNDTMWYZ9STWSS5axP910WQUT=JcQ@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
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<[email protected]>
Hi Tomas,
>
> Right. I'm still not convinced if this makes any difference, or whether
> this alignment was merely a consequence of using ShmemAlloc(). I don't
> want to make this harder to understand unnecessarily.
>
Yeah, it makes sense.
> Let's keep this simple - without additional alignment. I'll think about
> it a bit more, and maybe add it before commit.
>
OK.
>
>
> > I will improve the comment in the next version.
> >
>
> OK. Do we even need to pass nelem_alloc to hash_get_init_size? It's not
> really used except for this bit:
>
> + if (init_size > nelem_alloc)
> + element_alloc = false;
>
> Can't we determine before calling the function, to make it a bit less
> confusing?
>
Yes, we could determine whether the pre-allocated elements are zero before
calling the function, I have fixed it accordingly in the attached 0001
patch.
Now, there's no need to pass `nelem_alloc` as a parameter. Instead, I've
passed this information as a boolean variable-initial_elems. If it is
false,
no elements are pre-allocated.
Please find attached the v7-series, which incorporates your review patches
and addresses a few remaining comments.
Thank you,
Rahila Syed
Attachments:
[application/octet-stream] v7-0002-Replace-ShmemAlloc-calls-by-ShmemInitStruct.patch (7.0K, 3-v7-0002-Replace-ShmemAlloc-calls-by-ShmemInitStruct.patch)
download | inline diff:
From dfb7731cd9f4687f4d90a5210fb32c3a78fc4a5f Mon Sep 17 00:00:00 2001
From: Rahila Syed <[email protected]>
Date: Mon, 31 Mar 2025 03:45:50 +0530
Subject: [PATCH 2/3] Replace ShmemAlloc calls by ShmemInitStruct
The shared memory allocated by ShmemAlloc is not tracked
by pg_shmem_allocations. This commit replaces most of the
calls to ShmemAlloc by ShmemInitStruct to associate a name
with the allocations and ensure that they get tracked by
pg_shmem_allocations. It also merges several smaller
ShmemAlloc calls into larger ShmemInitStruct to allocate
and track all the related memory allocations under single
call.
---
src/backend/storage/lmgr/predicate.c | 30 ++++++++++-----
src/backend/storage/lmgr/proc.c | 57 +++++++++++++++++++++++-----
2 files changed, 67 insertions(+), 20 deletions(-)
diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c
index 5b21a05398..d82114ffca 100644
--- a/src/backend/storage/lmgr/predicate.c
+++ b/src/backend/storage/lmgr/predicate.c
@@ -1226,14 +1226,21 @@ PredicateLockShmemInit(void)
*/
max_table_size *= 10;
+ requestSize = add_size(PredXactListDataSize,
+ (mul_size((Size) max_table_size,
+ sizeof(SERIALIZABLEXACT))));
+
PredXact = ShmemInitStruct("PredXactList",
- PredXactListDataSize,
+ requestSize,
&found);
Assert(found == IsUnderPostmaster);
if (!found)
{
int i;
+ /* clean everything, both the header and the element */
+ memset(PredXact, 0, requestSize);
+
dlist_init(&PredXact->availableList);
dlist_init(&PredXact->activeList);
PredXact->SxactGlobalXmin = InvalidTransactionId;
@@ -1242,11 +1249,9 @@ PredicateLockShmemInit(void)
PredXact->LastSxactCommitSeqNo = FirstNormalSerCommitSeqNo - 1;
PredXact->CanPartialClearThrough = 0;
PredXact->HavePartialClearedThrough = 0;
- requestSize = mul_size((Size) max_table_size,
- sizeof(SERIALIZABLEXACT));
- PredXact->element = ShmemAlloc(requestSize);
+ PredXact->element
+ = (SERIALIZABLEXACT *) ((char *) PredXact + PredXactListDataSize);
/* Add all elements to available list, clean. */
- memset(PredXact->element, 0, requestSize);
for (i = 0; i < max_table_size; i++)
{
LWLockInitialize(&PredXact->element[i].perXactPredicateListLock,
@@ -1300,20 +1305,25 @@ PredicateLockShmemInit(void)
*/
max_table_size *= 5;
+ requestSize = RWConflictPoolHeaderDataSize +
+ mul_size((Size) max_table_size,
+ RWConflictDataSize);
+
RWConflictPool = ShmemInitStruct("RWConflictPool",
- RWConflictPoolHeaderDataSize,
+ requestSize,
&found);
Assert(found == IsUnderPostmaster);
if (!found)
{
int i;
+ /* clean everything, including the elements */
+ memset(RWConflictPool, 0, requestSize);
+
dlist_init(&RWConflictPool->availableList);
- requestSize = mul_size((Size) max_table_size,
- RWConflictDataSize);
- RWConflictPool->element = ShmemAlloc(requestSize);
+ RWConflictPool->element = (RWConflict) ((char *) RWConflictPool +
+ RWConflictPoolHeaderDataSize);
/* Add all elements to available list, clean. */
- memset(RWConflictPool->element, 0, requestSize);
for (i = 0; i < max_table_size; i++)
{
dlist_push_tail(&RWConflictPool->availableList,
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index 066319afe2..4e23c793f7 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -123,6 +123,25 @@ ProcGlobalShmemSize(void)
return size;
}
+/*
+ * Report shared-memory space needed by PGPROC.
+ */
+static Size
+PGProcShmemSize(void)
+{
+ Size size;
+ uint32 TotalProcs;
+
+ TotalProcs = MaxBackends + NUM_AUXILIARY_PROCS + max_prepared_xacts;
+
+ size = TotalProcs * sizeof(PGPROC);
+ size = add_size(size, TotalProcs * sizeof(*ProcGlobal->xids));
+ size = add_size(size, TotalProcs * sizeof(*ProcGlobal->subxidStates));
+ size = add_size(size, TotalProcs * sizeof(*ProcGlobal->statusFlags));
+
+ return size;
+}
+
/*
* Report number of semaphores needed by InitProcGlobal.
*/
@@ -175,6 +194,8 @@ InitProcGlobal(void)
*fpEndPtr PG_USED_FOR_ASSERTS_ONLY;
Size fpLockBitsSize,
fpRelIdSize;
+ Size requestSize;
+ char *ptr;
/* Create the ProcGlobal shared structure */
ProcGlobal = (PROC_HDR *)
@@ -204,7 +225,15 @@ InitProcGlobal(void)
* with a single freelist.) Each PGPROC structure is dedicated to exactly
* one of these purposes, and they do not move between groups.
*/
- procs = (PGPROC *) ShmemAlloc(TotalProcs * sizeof(PGPROC));
+ requestSize = PGProcShmemSize();
+
+ ptr = ShmemInitStruct("PGPROC structures",
+ requestSize,
+ &found);
+
+ procs = (PGPROC *) ptr;
+ ptr = (char *) ptr + TotalProcs * sizeof(PGPROC);
+
MemSet(procs, 0, TotalProcs * sizeof(PGPROC));
ProcGlobal->allProcs = procs;
/* XXX allProcCount isn't really all of them; it excludes prepared xacts */
@@ -213,17 +242,21 @@ InitProcGlobal(void)
/*
* Allocate arrays mirroring PGPROC fields in a dense manner. See
* PROC_HDR.
- *
- * XXX: It might make sense to increase padding for these arrays, given
- * how hotly they are accessed.
*/
- ProcGlobal->xids =
- (TransactionId *) ShmemAlloc(TotalProcs * sizeof(*ProcGlobal->xids));
+ ProcGlobal->xids = (TransactionId *) ptr;
MemSet(ProcGlobal->xids, 0, TotalProcs * sizeof(*ProcGlobal->xids));
- ProcGlobal->subxidStates = (XidCacheStatus *) ShmemAlloc(TotalProcs * sizeof(*ProcGlobal->subxidStates));
+ ptr = (char *) ptr + (TotalProcs * sizeof(*ProcGlobal->xids));
+
+ ProcGlobal->subxidStates = (XidCacheStatus *) ptr;
MemSet(ProcGlobal->subxidStates, 0, TotalProcs * sizeof(*ProcGlobal->subxidStates));
- ProcGlobal->statusFlags = (uint8 *) ShmemAlloc(TotalProcs * sizeof(*ProcGlobal->statusFlags));
+ ptr = (char *) ptr + (TotalProcs * sizeof(*ProcGlobal->subxidStates));
+
+ ProcGlobal->statusFlags = (uint8 *) ptr;
MemSet(ProcGlobal->statusFlags, 0, TotalProcs * sizeof(*ProcGlobal->statusFlags));
+ ptr = (char *) ptr + (TotalProcs * sizeof(*ProcGlobal->statusFlags));
+
+ /* make sure wer didn't overflow */
+ Assert((ptr > (char *) procs) && (ptr <= (char *) procs + requestSize));
/*
* Allocate arrays for fast-path locks. Those are variable-length, so
@@ -233,7 +266,9 @@ InitProcGlobal(void)
fpLockBitsSize = MAXALIGN(FastPathLockGroupsPerBackend * sizeof(uint64));
fpRelIdSize = MAXALIGN(FastPathLockSlotsPerBackend() * sizeof(Oid));
- fpPtr = ShmemAlloc(TotalProcs * (fpLockBitsSize + fpRelIdSize));
+ fpPtr = ShmemInitStruct("Fast path lock arrays",
+ TotalProcs * (fpLockBitsSize + fpRelIdSize),
+ &found);
MemSet(fpPtr, 0, TotalProcs * (fpLockBitsSize + fpRelIdSize));
/* For asserts checking we did not overflow. */
@@ -330,7 +365,9 @@ InitProcGlobal(void)
PreparedXactProcs = &procs[MaxBackends + NUM_AUXILIARY_PROCS];
/* Create ProcStructLock spinlock, too */
- ProcStructLock = (slock_t *) ShmemAlloc(sizeof(slock_t));
+ ProcStructLock = (slock_t *) ShmemInitStruct("ProcStructLock spinlock",
+ sizeof(slock_t),
+ &found);
SpinLockInit(ProcStructLock);
}
--
2.34.1
[application/octet-stream] v7-0003-Add-cacheline-padding-between-heavily-accessed-array.patch (2.1K, 4-v7-0003-Add-cacheline-padding-between-heavily-accessed-array.patch)
download | inline diff:
From 61712f86abd9edae190d27dc08be7b9753751a1d Mon Sep 17 00:00:00 2001
From: Rahila Syed <[email protected]>
Date: Mon, 31 Mar 2025 04:27:43 +0530
Subject: [PATCH 3/3] Add cacheline padding between heavily accessed arrays
---
src/backend/storage/lmgr/proc.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index 4e23c793f7..8363e2f61d 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -134,9 +134,9 @@ PGProcShmemSize(void)
TotalProcs = MaxBackends + NUM_AUXILIARY_PROCS + max_prepared_xacts;
- size = TotalProcs * sizeof(PGPROC);
- size = add_size(size, TotalProcs * sizeof(*ProcGlobal->xids));
- size = add_size(size, TotalProcs * sizeof(*ProcGlobal->subxidStates));
+ size = CACHELINEALIGN(TotalProcs * sizeof(PGPROC));
+ size = add_size(size, CACHELINEALIGN(TotalProcs * sizeof(*ProcGlobal->xids)));
+ size = add_size(size, CACHELINEALIGN(TotalProcs * sizeof(*ProcGlobal->subxidStates)));
size = add_size(size, TotalProcs * sizeof(*ProcGlobal->statusFlags));
return size;
@@ -232,7 +232,7 @@ InitProcGlobal(void)
&found);
procs = (PGPROC *) ptr;
- ptr = (char *) ptr + TotalProcs * sizeof(PGPROC);
+ ptr = (char *) ptr + CACHELINEALIGN(TotalProcs * sizeof(PGPROC));
MemSet(procs, 0, TotalProcs * sizeof(PGPROC));
ProcGlobal->allProcs = procs;
@@ -245,11 +245,11 @@ InitProcGlobal(void)
*/
ProcGlobal->xids = (TransactionId *) ptr;
MemSet(ProcGlobal->xids, 0, TotalProcs * sizeof(*ProcGlobal->xids));
- ptr = (char *) ptr + (TotalProcs * sizeof(*ProcGlobal->xids));
+ ptr = (char *) ptr + CACHELINEALIGN(TotalProcs * sizeof(*ProcGlobal->xids));
ProcGlobal->subxidStates = (XidCacheStatus *) ptr;
MemSet(ProcGlobal->subxidStates, 0, TotalProcs * sizeof(*ProcGlobal->subxidStates));
- ptr = (char *) ptr + (TotalProcs * sizeof(*ProcGlobal->subxidStates));
+ ptr = (char *) ptr + CACHELINEALIGN(TotalProcs * sizeof(*ProcGlobal->subxidStates));
ProcGlobal->statusFlags = (uint8 *) ptr;
MemSet(ProcGlobal->statusFlags, 0, TotalProcs * sizeof(*ProcGlobal->statusFlags));
--
2.34.1
[application/octet-stream] v7-0001-Account-for-all-the-shared-memory-allocated-by-hash_.patch (15.9K, 5-v7-0001-Account-for-all-the-shared-memory-allocated-by-hash_.patch)
download | inline diff:
From 4cce66bdfbb53b7ef3d9a7058f5979ac3b4dc89f Mon Sep 17 00:00:00 2001
From: Rahila Syed <[email protected]>
Date: Mon, 31 Mar 2025 03:23:20 +0530
Subject: [PATCH 1/3] Account for all the shared memory allocated by
hash_create
pg_shmem_allocations tracks the memory allocated by ShmemInitStruct,
which, in case of shared hash tables, only covers memory allocated
to the hash directory and header structure. The hash segments and
buckets are allocated using ShmemAllocNoError which does not attribute
the allocations to the hash table name. Thus, these allocations are
not tracked in pg_shmem_allocations.
Allocate memory for segments, buckets and elements together with the
directory and header structures. This results in the existing ShmemIndex
entries to reflect size of hash table more accurately, thus improving
the pg_shmem_allocation monitoring. Also, make this change for non-
shared hash table since they both share the hash_create code.
---
src/backend/storage/ipc/shmem.c | 4 +-
src/backend/utils/hash/dynahash.c | 283 +++++++++++++++++++++++-------
src/include/utils/hsearch.h | 3 +-
3 files changed, 222 insertions(+), 68 deletions(-)
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index 895a43fb39..3c030d5743 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -73,6 +73,7 @@
#include "storage/shmem.h"
#include "storage/spin.h"
#include "utils/builtins.h"
+#include "utils/dynahash.h"
static void *ShmemAllocRaw(Size size, Size *allocated_size);
@@ -346,7 +347,8 @@ ShmemInitHash(const char *name, /* table string name for shmem index */
/* look it up in the shmem index */
location = ShmemInitStruct(name,
- hash_get_shared_size(infoP, hash_flags),
+ hash_get_init_size(infoP, hash_flags,
+ true, init_size),
&found);
/*
diff --git a/src/backend/utils/hash/dynahash.c b/src/backend/utils/hash/dynahash.c
index 3f25929f2d..3dede9caa5 100644
--- a/src/backend/utils/hash/dynahash.c
+++ b/src/backend/utils/hash/dynahash.c
@@ -260,12 +260,36 @@ static long hash_accesses,
hash_expansions;
#endif
+#define HASH_DIRECTORY_PTR(hashp) \
+ (((char *) (hashp)->hctl) + sizeof(HASHHDR))
+
+#define HASH_SEGMENT_OFFSET(hctl, idx) \
+ (sizeof(HASHHDR) + \
+ ((hctl)->dsize * sizeof(HASHSEGMENT)) + \
+ ((hctl)->ssize * (idx) * sizeof(HASHBUCKET)))
+
+#define HASH_SEGMENT_PTR(hashp, idx) \
+ ((char *) (hashp)->hctl + HASH_SEGMENT_OFFSET((hashp)->hctl, (idx)))
+
+#define HASH_SEGMENT_SIZE(hashp) \
+ ((hashp)->ssize * sizeof(HASHBUCKET))
+
+#define HASH_ELEMENTS_PTR(hashp, nsegs) \
+ ((char *) (hashp)->hctl + HASH_SEGMENT_OFFSET((hashp)->hctl, nsegs))
+
+/* Each element has a HASHELEMENT header plus user data. */
+#define HASH_ELEMENT_SIZE(hctl) \
+ (MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN((hctl)->entrysize))
+
+#define HASH_ELEMENT_NEXT(hctl, num, ptr) \
+ ((char *) (ptr) + ((num) * HASH_ELEMENT_SIZE(hctl)))
+
/*
* Private function prototypes
*/
static void *DynaHashAlloc(Size size);
static HASHSEGMENT seg_alloc(HTAB *hashp);
-static bool element_alloc(HTAB *hashp, int nelem, int freelist_idx);
+static HASHELEMENT *element_alloc(HTAB *hashp, int nelem);
static bool dir_realloc(HTAB *hashp);
static bool expand_table(HTAB *hashp);
static HASHBUCKET get_hash_entry(HTAB *hashp, int freelist_idx);
@@ -281,6 +305,11 @@ static void register_seq_scan(HTAB *hashp);
static void deregister_seq_scan(HTAB *hashp);
static bool has_seq_scans(HTAB *hashp);
+static void compute_buckets_and_segs(long nelem, long num_partitions,
+ long ssize,
+ int *nbuckets, int *nsegments);
+static void element_add(HTAB *hashp, HASHELEMENT *firstElement,
+ int nelem, int freelist_idx);
/*
* memory allocation support
@@ -353,6 +382,8 @@ hash_create(const char *tabname, long nelem, const HASHCTL *info, int flags)
{
HTAB *hashp;
HASHHDR *hctl;
+ int nelem_batch;
+ bool initial_elems = false;
/*
* Hash tables now allocate space for key and data, but you have to say
@@ -507,9 +538,35 @@ hash_create(const char *tabname, long nelem, const HASHCTL *info, int flags)
hashp->isshared = false;
}
+ /* Choose the number of entries to allocate at a time. */
+ nelem_batch = choose_nelem_alloc(info->entrysize);
+
+ /*
+ * Calculate the number of elements to allocate
+ *
+ * For a shared hash table, preallocate the requested number of elements.
+ * This reduces problems with run-time out-of-shared-memory conditions.
+ *
+ * For a non-shared hash table, preallocate the requested number of
+ * elements if it's less than our chosen nelem_alloc. This avoids wasting
+ * space if the caller correctly estimates a small table size.
+ */
+ if ((flags & HASH_SHARED_MEM) ||
+ nelem < nelem_batch)
+ initial_elems = true;
+ else
+ initial_elems = false;
+
+ /*
+ * Allocate the memory needed for hash header, directory, segments and
+ * elements together. Use pointer arithmetic to arrive at the start of
+ * each of these structures later.
+ */
if (!hashp->hctl)
{
- hashp->hctl = (HASHHDR *) hashp->alloc(sizeof(HASHHDR));
+ Size size = hash_get_init_size(info, flags, initial_elems, nelem);
+
+ hashp->hctl = (HASHHDR *) hashp->alloc(size);
if (!hashp->hctl)
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -558,6 +615,9 @@ hash_create(const char *tabname, long nelem, const HASHCTL *info, int flags)
hctl->keysize = info->keysize;
hctl->entrysize = info->entrysize;
+ /* remember how many elements to allocate at once */
+ hctl->nelem_alloc = nelem_batch;
+
/* make local copies of heavily-used constant fields */
hashp->keysize = hctl->keysize;
hashp->ssize = hctl->ssize;
@@ -567,14 +627,6 @@ hash_create(const char *tabname, long nelem, const HASHCTL *info, int flags)
if (!init_htab(hashp, nelem))
elog(ERROR, "failed to initialize hash table \"%s\"", hashp->tabname);
- /*
- * For a shared hash table, preallocate the requested number of elements.
- * This reduces problems with run-time out-of-shared-memory conditions.
- *
- * For a non-shared hash table, preallocate the requested number of
- * elements if it's less than our chosen nelem_alloc. This avoids wasting
- * space if the caller correctly estimates a small table size.
- */
if ((flags & HASH_SHARED_MEM) ||
nelem < hctl->nelem_alloc)
{
@@ -582,6 +634,9 @@ hash_create(const char *tabname, long nelem, const HASHCTL *info, int flags)
freelist_partitions,
nelem_alloc,
nelem_alloc_first;
+ void *ptr = NULL;
+ int nsegs;
+ int nbuckets;
/*
* If hash table is partitioned, give each freelist an equal share of
@@ -606,14 +661,31 @@ hash_create(const char *tabname, long nelem, const HASHCTL *info, int flags)
else
nelem_alloc_first = nelem_alloc;
+ /*
+ * Calculate the offset at which to find the first partition of
+ * elements. We have to skip space for the header, segments and
+ * buckets.
+ */
+ compute_buckets_and_segs(nelem, hctl->num_partitions, hctl->ssize,
+ &nbuckets, &nsegs);
+
+ ptr = HASH_ELEMENTS_PTR(hashp, nsegs);
+
+ /*
+ * Assign the correct location of each parition within a pre-allocated
+ * buffer.
+ *
+ * Actual memory allocation happens in ShmemInitHash for shared hash
+ * tables or earlier in this function for non-shared hash tables.
+ *
+ * We just need to split that allocation into per-batch freelists.
+ */
for (i = 0; i < freelist_partitions; 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")));
+ element_add(hashp, (HASHELEMENT *) ptr, temp, i);
+ ptr = HASH_ELEMENT_NEXT(hctl, temp, ptr);
}
}
@@ -701,30 +773,12 @@ init_htab(HTAB *hashp, long nelem)
for (i = 0; i < NUM_FREELISTS; i++)
SpinLockInit(&(hctl->freeList[i].mutex));
- /*
- * Allocate space for the next greater power of two number of buckets,
- * assuming a desired maximum load factor of 1.
- */
- nbuckets = next_pow2_int(nelem);
-
- /*
- * In a partitioned table, nbuckets must be at least equal to
- * num_partitions; were it less, keys with apparently different partition
- * numbers would map to the same bucket, breaking partition independence.
- * (Normally nbuckets will be much bigger; this is just a safety check.)
- */
- while (nbuckets < hctl->num_partitions)
- nbuckets <<= 1;
+ compute_buckets_and_segs(nelem, hctl->num_partitions, hctl->ssize,
+ &nbuckets, &nsegs);
hctl->max_bucket = hctl->low_mask = nbuckets - 1;
hctl->high_mask = (nbuckets << 1) - 1;
- /*
- * Figure number of directory segments needed, round up to a power of 2
- */
- nsegs = (nbuckets - 1) / hctl->ssize + 1;
- nsegs = next_pow2_int(nsegs);
-
/*
* Make sure directory is big enough. If pre-allocated directory is too
* small, choke (caller screwed up).
@@ -737,26 +791,25 @@ init_htab(HTAB *hashp, long nelem)
return false;
}
- /* Allocate a directory */
+ /*
+ * Assign a directory by making it point to the correct location in the
+ * pre-allocated buffer.
+ */
if (!(hashp->dir))
{
CurrentDynaHashCxt = hashp->hcxt;
- hashp->dir = (HASHSEGMENT *)
- hashp->alloc(hctl->dsize * sizeof(HASHSEGMENT));
- if (!hashp->dir)
- return false;
+ hashp->dir = (HASHSEGMENT *) HASH_DIRECTORY_PTR(hashp);
}
- /* Allocate initial segments */
+ /* Assign initial segments, which are also pre-allocated */
+ i = 0;
for (segp = hashp->dir; hctl->nsegs < nsegs; hctl->nsegs++, segp++)
{
- *segp = seg_alloc(hashp);
- if (*segp == NULL)
- return false;
+ *segp = (HASHSEGMENT) HASH_SEGMENT_PTR(hashp, i++);
+ MemSet(*segp, 0, HASH_SEGMENT_SIZE(hashp));
}
- /* Choose number of entries to allocate at a time */
- hctl->nelem_alloc = choose_nelem_alloc(hctl->entrysize);
+ Assert(i == nsegs);
#ifdef HASH_DEBUG
fprintf(stderr, "init_htab:\n%s%p\n%s%ld\n%s%ld\n%s%d\n%s%ld\n%s%u\n%s%x\n%s%x\n%s%ld\n",
@@ -846,16 +899,70 @@ hash_select_dirsize(long num_entries)
}
/*
- * Compute the required initial memory allocation for a shared-memory
- * hashtable with the given parameters. We need space for the HASHHDR
- * and for the (non expansible) directory.
+ * Compute the required initial memory allocation for a hashtable with the given
+ * parameters. The hash table may be shared or private. We need space for the
+ * HASHHDR, for the directory, segments and the init_size elements in buckets.
+ *
+ * For shared hash tables the directory size is non-expansive.
+ *
+ * nelem is total number of elements requested during hash table creation.
+ *
+ * initial_nelems is true if it is decided to pre-allocate elements and false
+ * otherwise.
+ *
+ * For a shared hash table initial_elems is always true.
*/
Size
-hash_get_shared_size(HASHCTL *info, int flags)
+hash_get_init_size(const HASHCTL *info, int flags, bool initial_elems, long nelem)
{
- Assert(flags & HASH_DIRSIZE);
- Assert(info->dsize == info->max_dsize);
- return sizeof(HASHHDR) + info->dsize * sizeof(HASHSEGMENT);
+ int nbuckets;
+ int nsegs;
+ int num_partitions;
+ long ssize;
+ long dsize;
+ Size elementSize = HASH_ELEMENT_SIZE(info);
+ int init_size = 0;
+
+ if (flags & HASH_SHARED_MEM)
+ {
+ Assert(flags & HASH_DIRSIZE);
+ Assert(info->dsize == info->max_dsize);
+ }
+
+ /* Non-shared hash tables may not specify dir size */
+ if (!(flags & HASH_DIRSIZE))
+ {
+ dsize = DEF_DIRSIZE;
+ }
+ else
+ dsize = info->dsize;
+
+ if (flags & HASH_PARTITION)
+ {
+ num_partitions = info->num_partitions;
+
+ /* Number of entries should be atleast equal to the freelists */
+ if (nelem < NUM_FREELISTS)
+ nelem = NUM_FREELISTS;
+ }
+ else
+ num_partitions = 0;
+
+ if (flags & HASH_SEGMENT)
+ ssize = info->ssize;
+ else
+ ssize = DEF_SEGSIZE;
+
+ compute_buckets_and_segs(nelem, num_partitions, ssize,
+ &nbuckets, &nsegs);
+
+ /* initial_elems as false indicates no elements are to be pre-allocated */
+ if (initial_elems)
+ init_size = nelem;
+
+ return sizeof(HASHHDR) + dsize * sizeof(HASHSEGMENT)
+ + sizeof(HASHBUCKET) * ssize * nsegs
+ + init_size * elementSize;
}
@@ -1285,7 +1392,7 @@ get_hash_entry(HTAB *hashp, int freelist_idx)
* Failing because the needed element is in a different freelist is
* not acceptable.
*/
- if (!element_alloc(hashp, hctl->nelem_alloc, freelist_idx))
+ if ((newElement = element_alloc(hashp, hctl->nelem_alloc)) == NULL)
{
int borrow_from_idx;
@@ -1322,6 +1429,7 @@ get_hash_entry(HTAB *hashp, int freelist_idx)
/* no elements available to borrow either, so out of memory */
return NULL;
}
+ element_add(hashp, newElement, hctl->nelem_alloc, freelist_idx);
}
/* remove entry from freelist, bump nentries */
@@ -1700,29 +1808,43 @@ seg_alloc(HTAB *hashp)
}
/*
- * allocate some new elements and link them into the indicated free list
+ * allocate some new elements
*/
-static bool
-element_alloc(HTAB *hashp, int nelem, int freelist_idx)
+static HASHELEMENT *
+element_alloc(HTAB *hashp, int nelem)
{
HASHHDR *hctl = hashp->hctl;
Size elementSize;
- HASHELEMENT *firstElement;
- HASHELEMENT *tmpElement;
- HASHELEMENT *prevElement;
- int i;
+ HASHELEMENT *firstElement = NULL;
if (hashp->isfixed)
- return false;
+ return NULL;
/* Each element has a HASHELEMENT header plus user data. */
- elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(hctl->entrysize);
-
+ elementSize = HASH_ELEMENT_SIZE(hctl);
CurrentDynaHashCxt = hashp->hcxt;
firstElement = (HASHELEMENT *) hashp->alloc(nelem * elementSize);
if (!firstElement)
- return false;
+ return NULL;
+
+ return firstElement;
+}
+
+/*
+ * link the elements allocated by element_alloc into the indicated free list
+ */
+static void
+element_add(HTAB *hashp, HASHELEMENT *firstElement, int nelem, int freelist_idx)
+{
+ HASHHDR *hctl = hashp->hctl;
+ Size elementSize;
+ HASHELEMENT *tmpElement;
+ HASHELEMENT *prevElement;
+ int i;
+
+ /* Each element has a HASHELEMENT header plus user data. */
+ elementSize = HASH_ELEMENT_SIZE(hctl);
/* prepare to link all the new entries into the freelist */
prevElement = NULL;
@@ -1744,8 +1866,6 @@ element_alloc(HTAB *hashp, int nelem, int freelist_idx)
if (IS_PARTITIONED(hctl))
SpinLockRelease(&hctl->freeList[freelist_idx].mutex);
-
- return true;
}
/*
@@ -1957,3 +2077,34 @@ AtEOSubXact_HashTables(bool isCommit, int nestDepth)
}
}
}
+
+/*
+ * Calculate the number of buckets and segments to store the given
+ * number of elements in a hash table. Segments contain buckets which
+ * in turn contain elements.
+ */
+static void
+compute_buckets_and_segs(long nelem, long num_partitions, long ssize,
+ int *nbuckets, int *nsegments)
+{
+ /*
+ * Allocate space for the next greater power of two number of buckets,
+ * assuming a desired maximum load factor of 1.
+ */
+ *nbuckets = next_pow2_int(nelem);
+
+ /*
+ * In a partitioned table, nbuckets must be at least equal to
+ * num_partitions; were it less, keys with apparently different partition
+ * numbers would map to the same bucket, breaking partition independence.
+ * (Normally nbuckets will be much bigger; this is just a safety check.)
+ */
+ while ((*nbuckets) < num_partitions)
+ (*nbuckets) <<= 1;
+
+ /*
+ * Figure number of directory segments needed, round up to a power of 2
+ */
+ *nsegments = ((*nbuckets) - 1) / ssize + 1;
+ *nsegments = next_pow2_int(*nsegments);
+}
diff --git a/src/include/utils/hsearch.h b/src/include/utils/hsearch.h
index 932cc4f34d..4d5f09081b 100644
--- a/src/include/utils/hsearch.h
+++ b/src/include/utils/hsearch.h
@@ -151,7 +151,8 @@ extern void hash_seq_term(HASH_SEQ_STATUS *status);
extern void hash_freeze(HTAB *hashp);
extern Size hash_estimate_size(long num_entries, Size entrysize);
extern long hash_select_dirsize(long num_entries);
-extern Size hash_get_shared_size(HASHCTL *info, int flags);
+extern Size hash_get_init_size(const HASHCTL *info, int flags,
+ bool initial_elems, long nelem);
extern void AtEOXact_HashTables(bool isCommit);
extern void AtEOSubXact_HashTables(bool isCommit, int nestDepth);
--
2.34.1
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Subject: Re: Improve monitoring of shared memory allocations
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