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* [PATCH 3/9] Optimize allocations in bringetbitmap
@ 2020-09-13 10:12 Tomas Vondra <[email protected]>
0 siblings, 0 replies; 2+ messages in thread
From: Tomas Vondra @ 2020-09-13 10:12 UTC (permalink / raw)
The bringetbitmap function allocates memory for various purposes, which
may be quite expensive, depending on the number of scan keys. Instead of
allocating them separately, allocate one bit chunk of memory an carve it
into smaller pieces as needed - all the pieces have the same lifespan,
and it saves quite a bit of CPU and memory overhead.
Author: Tomas Vondra <[email protected]>
Discussion: https://postgr.es/m/[email protected]
---
src/backend/access/brin/brin.c | 62 +++++++++++++++++++++++++++-------
1 file changed, 49 insertions(+), 13 deletions(-)
diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index 14da9ed17f..3735c41788 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -373,6 +373,9 @@ bringetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
int *nkeys,
*nnullkeys;
int keyno;
+ char *ptr;
+ Size len;
+ char *tmp PG_USED_FOR_ASSERTS_ONLY;
opaque = (BrinOpaque *) scan->opaque;
bdesc = opaque->bo_bdesc;
@@ -398,11 +401,50 @@ bringetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
* Make room for per-attribute lists of scan keys that we'll pass to the
* consistent support procedure. We keep null and regular keys separate,
* so that we can easily pass regular keys to the consistent function.
+ *
+ * To reduce the allocation overhead, we allocate one big chunk and then
+ * carve it into smaller arrays ourselves. All the pieces have exactly
+ * the same lifetime, so that's OK.
*/
- keys = palloc0(sizeof(ScanKey *) * bdesc->bd_tupdesc->natts);
- nullkeys = palloc0(sizeof(ScanKey *) * bdesc->bd_tupdesc->natts);
- nkeys = palloc0(sizeof(int) * bdesc->bd_tupdesc->natts);
- nnullkeys = palloc0(sizeof(int) * bdesc->bd_tupdesc->natts);
+ len =
+ /* regular keys */
+ MAXALIGN(sizeof(ScanKey *) * bdesc->bd_tupdesc->natts) +
+ MAXALIGN(sizeof(ScanKey) * scan->numberOfKeys * bdesc->bd_tupdesc->natts) +
+ MAXALIGN(sizeof(int) * bdesc->bd_tupdesc->natts) +
+ /* NULL keys */
+ MAXALIGN(sizeof(ScanKey *) * bdesc->bd_tupdesc->natts) +
+ MAXALIGN(sizeof(ScanKey) * scan->numberOfKeys * bdesc->bd_tupdesc->natts) +
+ MAXALIGN(sizeof(int) * bdesc->bd_tupdesc->natts);
+
+ ptr = palloc(len);
+ tmp = ptr;
+
+ keys = (ScanKey **) ptr;
+ ptr += MAXALIGN(sizeof(ScanKey *) * bdesc->bd_tupdesc->natts);
+
+ nullkeys = (ScanKey **) ptr;
+ ptr += MAXALIGN(sizeof(ScanKey *) * bdesc->bd_tupdesc->natts);
+
+ nkeys = (int *) ptr;
+ ptr += MAXALIGN(sizeof(int) * bdesc->bd_tupdesc->natts);
+
+ nnullkeys = (int *) ptr;
+ ptr += MAXALIGN(sizeof(int) * bdesc->bd_tupdesc->natts);
+
+ for (int i = 0; i < bdesc->bd_tupdesc->natts; i++)
+ {
+ keys[i] = (ScanKey *) ptr;
+ ptr += MAXALIGN(sizeof(ScanKey) * scan->numberOfKeys);
+
+ nullkeys[i] = (ScanKey *) ptr;
+ ptr += MAXALIGN(sizeof(ScanKey) * scan->numberOfKeys);
+ }
+
+ Assert(tmp + len == ptr);
+
+ /* zero the number of keys */
+ memset(nkeys, 0, sizeof(int) * bdesc->bd_tupdesc->natts);
+ memset(nnullkeys, 0, sizeof(int) * bdesc->bd_tupdesc->natts);
/*
* Preprocess the scan keys - split them into per-attribute arrays.
@@ -438,9 +480,9 @@ bringetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
{
FmgrInfo *tmp;
- /* No key/null arrays for this attribute. */
- Assert((keys[keyattno - 1] == NULL) && (nkeys[keyattno - 1] == 0));
- Assert((nullkeys[keyattno - 1] == NULL) && (nnullkeys[keyattno - 1] == 0));
+ /* First time we see this attribute, so no key/null keys. */
+ Assert(nkeys[keyattno - 1] == 0);
+ Assert(nnullkeys[keyattno - 1] == 0);
tmp = index_getprocinfo(idxRel, keyattno,
BRIN_PROCNUM_CONSISTENT);
@@ -451,17 +493,11 @@ bringetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
/* Add key to the proper per-attribute array. */
if (key->sk_flags & SK_ISNULL)
{
- if (!nullkeys[keyattno - 1])
- nullkeys[keyattno - 1] = palloc0(sizeof(ScanKey) * scan->numberOfKeys);
-
nullkeys[keyattno - 1][nnullkeys[keyattno - 1]] = key;
nnullkeys[keyattno - 1]++;
}
else
{
- if (!keys[keyattno - 1])
- keys[keyattno - 1] = palloc0(sizeof(ScanKey) * scan->numberOfKeys);
-
keys[keyattno - 1][nkeys[keyattno - 1]] = key;
nkeys[keyattno - 1]++;
}
--
2.26.2
--------------4B194FF8F3EA3786FF9EAE1F
Content-Type: text/x-patch; charset=UTF-8;
name="0002-Move-IS-NOT-NULL-handling-from-BRIN-support-20210203.patch"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
filename*0="0002-Move-IS-NOT-NULL-handling-from-BRIN-support-20210203.pa";
filename*1="tch"
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: using extended statistics to improve join estimates
@ 2022-01-04 23:55 Andres Freund <[email protected]>
0 siblings, 0 replies; 2+ messages in thread
From: Andres Freund @ 2022-01-04 23:55 UTC (permalink / raw)
To: Tomas Vondra <[email protected]>; +Cc: Justin Pryzby <[email protected]>; pgsql-hackers
On 2022-01-01 18:21:06 +0100, Tomas Vondra wrote:
> Here's an updated patch, rebased and fixing a couple typos reported by
> Justin Pryzby directly.
FWIW, cfbot reports a few compiler warnings:
https://cirrus-ci.com/task/6067262669979648?logs=gcc_warning#L505
[18:52:15.132] time make -s -j${BUILD_JOBS} world-bin
[18:52:22.697] mcv.c: In function ‘mcv_combine_simple’:
[18:52:22.697] mcv.c:2787:7: error: ‘reverse’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
[18:52:22.697] 2787 | if (reverse)
[18:52:22.697] | ^
[18:52:22.697] mcv.c:2766:27: error: ‘index’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
[18:52:22.697] 2766 | if (mcv->items[i].isnull[index])
[18:52:22.697] | ^
Greetings,
Andres Freund
^ permalink raw reply [nested|flat] 2+ messages in thread
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2020-09-13 10:12 [PATCH 3/9] Optimize allocations in bringetbitmap Tomas Vondra <[email protected]>
2022-01-04 23:55 Re: using extended statistics to improve join estimates Andres Freund <[email protected]>
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