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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: Tue, 1 Apr 2025 13:13:21 +0530
Message-ID: <CAH2L28vaktm0UXw19y22w+DThcqV80-UKtVfMxPeVw8ro2yTDg@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <CAH2L28vHzRankszhqz7deXURxKncxfirnuW68zD7+hVAqaS5GQ@mail.gmail.com>
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<[email protected]>
Hi,
I think it's almost committable. Attached is v8 with some minor review
> adjustments, and updated commit messages. Please read through those and
> feel free to suggest changes.
>
>
The changes look good to me.
About the following question.
/* XXX what about segment size? should check have HASH_SEGMENT? */
Do you mean for a shared hash table should the caller have specified
HASH_SEGMENT
in flags?
It appears that the current code does not require this change. All the
shared hash tables seem
to have the default segment size.
I left the comment as it is as I am not sure if you intend to remove it or
not.
> I still found the hash_get_init_size() comment unclear, and it also
> referenced init_size, which is no longer relevant. I improved the
> comment a bit (I find it useful to mimic comments of nearby functions,
> so I did that too here). The "initial_elems" name was a bit confusing,
> as it seemed to suggest "number of elements", but it's a simple flag. So
> I renamed it to "prealloc", which seems clearer to me. I also tweaked
> (reordered/reformatted) the conditions a bit.
I appreciate your edtis, the comment and code are clearer now.
PFA the patches after merging the review patches.
Thank you,
Rahila Syed
Attachments:
[application/octet-stream] v9-0001-Improve-acounting-for-memory-used-by-shared-hash-tab.patch (17.0K, 3-v9-0001-Improve-acounting-for-memory-used-by-shared-hash-tab.patch)
download | inline diff:
From 44a2882e490cd0cd43751d24a864ea24e2b20135 Mon Sep 17 00:00:00 2001
From: Rahila Syed <[email protected]>
Date: Tue, 1 Apr 2025 12:59:19 +0530
Subject: [PATCH 1/3] Improve acounting for memory used by shared hash tables
pg_shmem_allocations tracks the memory allocated by ShmemInitStruct(),
but for shared hash tables that covered only the header and hash
directory. The remaining parts (segments and buckets) were allocated
later using ShmemAlloc(), which does not update the shmem accounting.
Thus, these allocations were not shown in pg_shmem_allocations.
This commit improves the situation by allocating all the hash table
parts at once, using a single ShmemInitStruct() call. This way the
ShmemIndex entries (and thus pg_shmem_allocations) better reflect the
proper size of the hash table.
This affects allocations for private (non-shared) hash tables too, as
the hash_create() code is shared. For non-shared tables this however
makes no practical difference.
This changes the alignment a bit. ShmemAlloc() aligns the chunks using
CACHELINEALIGN(), which means some parts (header, directory, segments)
were aligned this way. Allocating all parts as a single chunks removes
this (implicit) alignment. We've considered adding explicit alignment,
but we've decided not to - it seems to be merely a coincidence due to
using the ShmemAlloc() API, not due to necessity.
Author: Rahila Syed <[email protected]>
Reviewed-by: Andres Freund <[email protected]>
Reviewed-by: Nazir Bilal Yavuz <[email protected]>
Reviewed-by: Tomas Vondra <[email protected]>
Discussion: https://postgr.es/m/CAH2L28vHzRankszhqz7deXURxKncxfirnuW68zD7+hVAqaS5GQ@mail.gmail.com
---
src/backend/storage/ipc/shmem.c | 4 +-
src/backend/utils/hash/dynahash.c | 286 +++++++++++++++++++++++-------
src/include/utils/hsearch.h | 3 +-
3 files changed, 225 insertions(+), 68 deletions(-)
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index 895a43fb39..8e19134cb5 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,
+ init_size, true),
&found);
/*
diff --git a/src/backend/utils/hash/dynahash.c b/src/backend/utils/hash/dynahash.c
index 3f25929f2d..0240a87139 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 prealloc;
/*
* Hash tables now allocate space for key and data, but you have to say
@@ -507,9 +538,31 @@ 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 private 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.
+ */
+ prealloc = (flags & HASH_SHARED_MEM) || (nelem < nelem_batch);
+
+ /*
+ * 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, nelem, prealloc);
+
+ hashp->hctl = (HASHHDR *) hashp->alloc(size);
if (!hashp->hctl)
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
@@ -558,6 +611,9 @@ 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 +623,6 @@ 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 +630,9 @@ 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 +657,32 @@ 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. We need to recalculate the number of segments, which we
+ * don't store anywhere.
+ */
+ 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 +770,12 @@ 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 +788,25 @@ 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 +896,76 @@ 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.
+ * hash_get_init_size -- determine memory needed for a new dynamic hash table
+ *
+ * info: hash table parameters
+ * flags: bitmask indicating which parameters to take from *info
+ * nelem: maximum number of elements expected
+ * prealloc: request preallocation of elements
+ *
+ * Compute the required initial memory allocation for a hashtable with the given
+ * parameters. We need space for the HASHHDR, for the directory, segments and
+ * preallocated elements.
+ *
+ * The hash table may be private or shared. For shared hash tables the directory
+ * size is non-expansive, and we preallocate all elements (nelem). For private
+ * hash tables, we preallocate elements only if the expected number of elements
+ * is small (less than nelem_alloc).
*/
Size
-hash_get_shared_size(HASHCTL *info, int flags)
+hash_get_init_size(const HASHCTL *info, int flags, long nelem, bool prealloc)
{
- 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);
+ long nelem_prealloc = 0;
+
+#ifdef USE_ASSERT_CHECKING
+ /* shared hash tables have non-expansive directory */
+ /* XXX what about segment size? should check have HASH_SEGMENT? */
+ if (flags & HASH_SHARED_MEM)
+ {
+ Assert(flags & HASH_DIRSIZE);
+ Assert(info->dsize == info->max_dsize);
+ Assert(prealloc);
+ }
+#endif
+
+ /* Non-shared hash tables may not specify dir size */
+ if (flags & HASH_DIRSIZE)
+ dsize = info->dsize;
+ else
+ dsize = DEF_DIRSIZE;
+
+ if (flags & HASH_SEGMENT)
+ ssize = info->ssize;
+ else
+ ssize = DEF_SEGSIZE;
+
+ 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;
+
+ compute_buckets_and_segs(nelem, num_partitions, ssize,
+ &nbuckets, &nsegs);
+
+ /* initial_elems as false indicates no elements are to be pre-allocated */
+ if (prealloc)
+ nelem_prealloc = nelem;
+
+ return sizeof(HASHHDR) + dsize * sizeof(HASHSEGMENT)
+ + sizeof(HASHBUCKET) * ssize * nsegs
+ + nelem_prealloc * elementSize;
}
@@ -1285,7 +1395,7 @@ 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 +1432,7 @@ 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 +1811,43 @@ 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 +1869,6 @@ element_alloc(HTAB *hashp, int nelem, int freelist_idx)
if (IS_PARTITIONED(hctl))
SpinLockRelease(&hctl->freeList[freelist_idx].mutex);
-
- return true;
}
/*
@@ -1957,3 +2080,34 @@ 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..5dc74db6e9 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,
+ long nelem, bool prealloc);
extern void AtEOXact_HashTables(bool isCommit);
extern void AtEOSubXact_HashTables(bool isCommit, int nestDepth);
--
2.34.1
[application/octet-stream] v9-0002-Improve-accounting-for-PredXactList-RWConflictPool-a.patch (7.5K, 4-v9-0002-Improve-accounting-for-PredXactList-RWConflictPool-a.patch)
download | inline diff:
From 14487eb068f434de48411727a32310bc9c3ef933 Mon Sep 17 00:00:00 2001
From: Rahila Syed <[email protected]>
Date: Tue, 1 Apr 2025 13:01:38 +0530
Subject: [PATCH 2/3] Improve accounting for PredXactList, RWConflictPool and
PGPROC
Various places allocated shared memory by first allocating a small chunk
using ShmemInitStruct(), followed by ShmemAlloc() calls to allocate more
memory. Unfortunately, ShmemAlloc() does not update ShmemIndex, so this
affected pg_shmem_allocations - it only shown the initial chunk.
This commit modifies the following allocations, to allocate everything
as a single chunk, and then split it internally.
- PredXactList
- RWConflictPool
- PGPROC structures
- Fast-Path lock arrays
Author: Rahila Syed <[email protected]>
Reviewed-by: Andres Freund <[email protected]>
Reviewed-by: Nazir Bilal Yavuz <[email protected]>
Reviewed-by: Tomas Vondra <[email protected]>
Discussion: https://postgr.es/m/CAH2L28vHzRankszhqz7deXURxKncxfirnuW68zD7+hVAqaS5GQ@mail.gmail.com
---
src/backend/storage/lmgr/predicate.c | 30 ++++++++-----
src/backend/storage/lmgr/proc.c | 63 +++++++++++++++++++++-------
2 files changed, 69 insertions(+), 24 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..ba1ac7e486 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 *)
@@ -204,8 +225,17 @@ 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));
- MemSet(procs, 0, TotalProcs * sizeof(PGPROC));
+ requestSize = PGProcShmemSize();
+
+ ptr = ShmemInitStruct("PGPROC structures",
+ requestSize,
+ &found);
+
+ MemSet(ptr, 0, requestSize);
+
+ procs = (PGPROC *) ptr;
+ ptr = (char *) ptr + TotalProcs * sizeof(PGPROC);
+
ProcGlobal->allProcs = procs;
/* XXX allProcCount isn't really all of them; it excludes prepared xacts */
ProcGlobal->allProcCount = MaxBackends + NUM_AUXILIARY_PROCS;
@@ -213,17 +243,18 @@ 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));
- MemSet(ProcGlobal->xids, 0, TotalProcs * sizeof(*ProcGlobal->xids));
- ProcGlobal->subxidStates = (XidCacheStatus *) ShmemAlloc(TotalProcs * sizeof(*ProcGlobal->subxidStates));
- MemSet(ProcGlobal->subxidStates, 0, TotalProcs * sizeof(*ProcGlobal->subxidStates));
- ProcGlobal->statusFlags = (uint8 *) ShmemAlloc(TotalProcs * sizeof(*ProcGlobal->statusFlags));
- MemSet(ProcGlobal->statusFlags, 0, TotalProcs * sizeof(*ProcGlobal->statusFlags));
+ ProcGlobal->xids = (TransactionId *) ptr;
+ ptr = (char *) ptr + (TotalProcs * sizeof(*ProcGlobal->xids));
+
+ ProcGlobal->subxidStates = (XidCacheStatus *) ptr;
+ ptr = (char *) ptr + (TotalProcs * sizeof(*ProcGlobal->subxidStates));
+
+ ProcGlobal->statusFlags = (uint8 *) ptr;
+ 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 +264,9 @@ 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 +363,9 @@ 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] v9-0003-Add-cacheline-padding-between-heavily-accessed-array.patch (2.0K, 5-v9-0003-Add-cacheline-padding-between-heavily-accessed-array.patch)
download | inline diff:
From 78a5cdd3d04498eeb11ec818913131d9b69613fb Mon Sep 17 00:00:00 2001
From: Rahila Syed <[email protected]>
Date: Tue, 1 Apr 2025 13:06:57 +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 ba1ac7e486..c39b51127a 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;
@@ -234,7 +234,7 @@ InitProcGlobal(void)
MemSet(ptr, 0, requestSize);
procs = (PGPROC *) ptr;
- ptr = (char *) ptr + TotalProcs * sizeof(PGPROC);
+ ptr = (char *) ptr + CACHELINEALIGN(TotalProcs * sizeof(PGPROC));
ProcGlobal->allProcs = procs;
/* XXX allProcCount isn't really all of them; it excludes prepared xacts */
@@ -245,10 +245,10 @@ InitProcGlobal(void)
* PROC_HDR.
*/
ProcGlobal->xids = (TransactionId *) ptr;
- ptr = (char *) ptr + (TotalProcs * sizeof(*ProcGlobal->xids));
+ ptr = (char *) ptr + CACHELINEALIGN(TotalProcs * sizeof(*ProcGlobal->xids));
ProcGlobal->subxidStates = (XidCacheStatus *) ptr;
- ptr = (char *) ptr + (TotalProcs * sizeof(*ProcGlobal->subxidStates));
+ ptr = (char *) ptr + CACHELINEALIGN(TotalProcs * sizeof(*ProcGlobal->subxidStates));
ProcGlobal->statusFlags = (uint8 *) ptr;
ptr = (char *) ptr + (TotalProcs * sizeof(*ProcGlobal->statusFlags));
--
2.34.1
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Subject: Re: Improve monitoring of shared memory allocations
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