From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Dean Rasheed <dean.a.rasheed@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Choosing values for multivariate MCV lists
Date: Mon, 24 Jun 2019 01:56:36 +0200
Message-ID: <20190623235636.s2wlndxdhdpjhowc@development> (raw)
In-Reply-To: <20190623234232.xkydftfd7uxexelo@development>
References: <20190618205920.qtlzcu73whfpfqne@development>
<CAEZATCWMDpQUmnSXtRCq_CxLXUoLETra=7SoQ3P5ydiFcse7wQ@mail.gmail.com>
<20190620223548.p22wj7uejbrhkglf@development>
<CAEZATCWqqB3R+Oewq2u_ByS01-12+M4=yRARVvdmx4R0ZO-RvQ@mail.gmail.com>
<20190622141052.5csokbp3sx577mub@development>
<CAEZATCVQYRScftGh-k_An8yo0d=GwNKzEUOR=t4g7Zw9Qd1=kQ@mail.gmail.com>
<20190623202319.4lcqsi5zc53hktda@development>
<20190623234232.xkydftfd7uxexelo@development>
On Mon, Jun 24, 2019 at 01:42:32AM +0200, Tomas Vondra wrote:
>On Sun, Jun 23, 2019 at 10:23:19PM +0200, Tomas Vondra wrote:
>>On Sun, Jun 23, 2019 at 08:48:26PM +0100, Dean Rasheed wrote:
>>>On Sat, 22 Jun 2019 at 15:10, Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:
>>>>One annoying thing I noticed is that the base_frequency tends to end up
>>>>being 0, most likely due to getting too small. It's a bit strange, though,
>>>>because with statistic target set to 10k the smallest frequency for a
>>>>single column is 1/3e6, so for 2 columns it'd be ~1/9e12 (which I think is
>>>>something the float8 can represent).
>>>>
>>>
>>>Yeah, it should be impossible for the base frequency to underflow to
>>>0. However, it looks like the problem is with mcv_list_items()'s use
>>>of %f to convert to text, which is pretty ugly.
>>>
>>
>>Yeah, I realized that too, eventually. One way to fix that would be
>>adding %.15f to the sprintf() call, but that just adds ugliness. It's
>>probably time to rewrite the function to build the tuple from datums,
>>instead of relying on BuildTupleFromCStrings.
>>
>
>OK, attached is a patch doing this. It's pretty simple, and it does
>resolve the issue with frequency precision.
>
>There's one issue with the signature, though - currently the function
>returns null flags as bool array, but values are returned as simple
>text value (formatted in array-like way, but still just a text).
>
>In the attached patch I've reworked both to proper arrays, but obviously
>that'd require a CATVERSION bump - and there's not much apetite for that
>past beta2, I suppose. So I'll just undo this bit.
>
Meh, I forgot to attach the patch, of couse ...
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
From 9aa3ce9bfdcab50a6d5dcf289bcf715e4a8aed9c Mon Sep 17 00:00:00 2001
From: Tomas Vondra <tomas@2ndquadrant.com>
Date: Mon, 24 Jun 2019 00:50:53 +0200
Subject: [PATCH 1/3] rework pg_mcv_list_items
---
src/backend/statistics/mcv.c | 106 ++++++++++++--------------------
src/include/catalog/pg_proc.dat | 2 +-
2 files changed, 42 insertions(+), 66 deletions(-)
diff --git a/src/backend/statistics/mcv.c b/src/backend/statistics/mcv.cindex 5fe61ea0a4..1b1a5c9846 100644--- a/src/backend/statistics/mcv.c+++ b/src/backend/statistics/mcv.c@@ -1134,9 +1134,6 @@ Datum
pg_stats_ext_mcvlist_items(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
- int call_cntr;- int max_calls;- AttInMetadata *attinmeta;
/* stuff done only on the first call of the function */
if (SRF_IS_FIRSTCALL())
@@ -1166,13 +1163,13 @@ pg_stats_ext_mcvlist_items(PG_FUNCTION_ARGS)
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("function returning record called in context "
"that cannot accept type record")));
+ tupdesc = BlessTupleDesc(tupdesc);
/*
* generate attribute metadata needed later to produce tuples from raw
* C strings
*/
- attinmeta = TupleDescGetAttInMetadata(tupdesc);- funcctx->attinmeta = attinmeta;+ funcctx->attinmeta = TupleDescGetAttInMetadata(tupdesc);
MemoryContextSwitchTo(oldcontext);
}
@@ -1180,18 +1177,17 @@ pg_stats_ext_mcvlist_items(PG_FUNCTION_ARGS)
/* stuff done on every call of the function */
funcctx = SRF_PERCALL_SETUP();
- call_cntr = funcctx->call_cntr;- max_calls = funcctx->max_calls;- attinmeta = funcctx->attinmeta;-- if (call_cntr < max_calls) /* do when there is more left to send */+ if (funcctx->call_cntr < funcctx->max_calls) /* do when there is more left to send */
{
- char **values;+ Datum values[5];+ bool nulls[5];
HeapTuple tuple;
Datum result;
+ int dims[1];+ int lbs[1];- StringInfoData itemValues;- StringInfoData itemNulls;+ Datum *itemNulls;+ Datum *itemValues;
int i;
@@ -1203,24 +1199,16 @@ pg_stats_ext_mcvlist_items(PG_FUNCTION_ARGS)
mcvlist = (MCVList *) funcctx->user_fctx;
- Assert(call_cntr < mcvlist->nitems);-- item = &mcvlist->items[call_cntr];-- /*- * Prepare a values array for building the returned tuple. This should- * be an array of C strings which will be processed later by the type- * input functions.- */- values = (char **) palloc0(5 * sizeof(char *));+ Assert(funcctx->call_cntr < mcvlist->nitems);- values[0] = (char *) palloc(64 * sizeof(char)); /* item index */- values[3] = (char *) palloc(64 * sizeof(char)); /* frequency */- values[4] = (char *) palloc(64 * sizeof(char)); /* base frequency */+ item = &mcvlist->items[funcctx->call_cntr];
outfuncs = (Oid *) palloc0(sizeof(Oid) * mcvlist->ndimensions);
fmgrinfo = (FmgrInfo *) palloc0(sizeof(FmgrInfo) * mcvlist->ndimensions);
+ itemValues = (Datum *) palloc(sizeof(Datum) * mcvlist->ndimensions);+ itemNulls = (Datum *) palloc(sizeof(Datum) * mcvlist->ndimensions);+
for (i = 0; i < mcvlist->ndimensions; i++)
{
bool isvarlena;
@@ -1230,61 +1218,49 @@ pg_stats_ext_mcvlist_items(PG_FUNCTION_ARGS)
fmgr_info(outfuncs[i], &fmgrinfo[i]);
}
- /* build the arrays of values / nulls */- initStringInfo(&itemValues);- initStringInfo(&itemNulls);-- appendStringInfoChar(&itemValues, '{');- appendStringInfoChar(&itemNulls, '{');-
for (i = 0; i < mcvlist->ndimensions; i++)
{
- Datum val,- valout;-- if (i > 0)- {- appendStringInfoString(&itemValues, ", ");- appendStringInfoString(&itemNulls, ", ");- }+ Datum valout;
if (item->isnull[i])
- valout = CStringGetDatum("NULL");+ valout = (Datum) 0;
else
- {- val = item->values[i];- valout = FunctionCall1(&fmgrinfo[i], val);- }+ valout = FunctionCall1(&fmgrinfo[i], item->values[i]);- appendStringInfoString(&itemValues, DatumGetCString(valout));- appendStringInfoString(&itemNulls, item->isnull[i] ? "t" : "f");+ itemNulls[i] = BoolGetDatum(item->isnull[i]);+ itemValues[i] = valout;
}
- appendStringInfoChar(&itemValues, '}');- appendStringInfoChar(&itemNulls, '}');+ dims[0] = mcvlist->ndimensions;+ lbs[0] = 1;++ values[0] = Int32GetDatum(funcctx->call_cntr);- snprintf(values[0], 64, "%d", call_cntr);- snprintf(values[3], 64, "%f", item->frequency);- snprintf(values[4], 64, "%f", item->base_frequency);+ values[1] = PointerGetDatum(construct_md_array(itemValues,+ item->isnull,+ 1,+ dims,+ lbs,+ CSTRINGOID, -2,+ false, 'c'));- values[1] = itemValues.data;- values[2] = itemNulls.data;+ values[2] = PointerGetDatum(construct_array(itemNulls,+ mcvlist->ndimensions,+ BOOLOID, sizeof(bool),+ true, 'c'));++ values[3] = Float8GetDatum(item->frequency);+ values[4] = Float8GetDatum(item->base_frequency);++ /* no NULLs in the tuple */+ memset(nulls, 0, sizeof(nulls));
/* build a tuple */
- tuple = BuildTupleFromCStrings(attinmeta, values);+ tuple = heap_form_tuple(funcctx->attinmeta->tupdesc, values, nulls);
/* make the tuple into a datum */
result = HeapTupleGetDatum(tuple);
- /* clean up (this is not really necessary) */- pfree(itemValues.data);- pfree(itemNulls.data);-- pfree(values[0]);- pfree(values[3]);- pfree(values[4]);- pfree(values);-
SRF_RETURN_NEXT(funcctx, result);
}
else /* do when there is no more left */
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.datindex 87335248a0..36ae2ac9d8 100644--- a/src/include/catalog/pg_proc.dat+++ b/src/include/catalog/pg_proc.dat@@ -5019,7 +5019,7 @@
{ oid => '3427', descr => 'details about MCV list items',
proname => 'pg_mcv_list_items', prorows => '1000', proretset => 't',
provolatile => 's', prorettype => 'record', proargtypes => 'pg_mcv_list',
- proallargtypes => '{pg_mcv_list,int4,text,_bool,float8,float8}',+ proallargtypes => '{pg_mcv_list,int4,_text,_bool,float8,float8}',
proargmodes => '{i,o,o,o,o,o}',
proargnames => '{mcv_list,index,values,nulls,frequency,base_frequency}',
prosrc => 'pg_stats_ext_mcvlist_items' },
--
2.20.1
Attachments:
[text/plain] 0001-rework-pg_mcv_list_items.patch (6.2K, ../20190623235636.s2wlndxdhdpjhowc@development/2-0001-rework-pg_mcv_list_items.patch)
download | inline diff:
From 9aa3ce9bfdcab50a6d5dcf289bcf715e4a8aed9c Mon Sep 17 00:00:00 2001
From: Tomas Vondra <tomas@2ndquadrant.com>
Date: Mon, 24 Jun 2019 00:50:53 +0200
Subject: [PATCH 1/3] rework pg_mcv_list_items
---
src/backend/statistics/mcv.c | 106 ++++++++++++--------------------
src/include/catalog/pg_proc.dat | 2 +-
2 files changed, 42 insertions(+), 66 deletions(-)
diff --git a/src/backend/statistics/mcv.c b/src/backend/statistics/mcv.cindex 5fe61ea0a4..1b1a5c9846 100644--- a/src/backend/statistics/mcv.c+++ b/src/backend/statistics/mcv.c@@ -1134,9 +1134,6 @@ Datum
pg_stats_ext_mcvlist_items(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
- int call_cntr;- int max_calls;- AttInMetadata *attinmeta;
/* stuff done only on the first call of the function */
if (SRF_IS_FIRSTCALL())
@@ -1166,13 +1163,13 @@ pg_stats_ext_mcvlist_items(PG_FUNCTION_ARGS)
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("function returning record called in context "
"that cannot accept type record")));
+ tupdesc = BlessTupleDesc(tupdesc);
/*
* generate attribute metadata needed later to produce tuples from raw
* C strings
*/
- attinmeta = TupleDescGetAttInMetadata(tupdesc);- funcctx->attinmeta = attinmeta;+ funcctx->attinmeta = TupleDescGetAttInMetadata(tupdesc);
MemoryContextSwitchTo(oldcontext);
}
@@ -1180,18 +1177,17 @@ pg_stats_ext_mcvlist_items(PG_FUNCTION_ARGS)
/* stuff done on every call of the function */
funcctx = SRF_PERCALL_SETUP();
- call_cntr = funcctx->call_cntr;- max_calls = funcctx->max_calls;- attinmeta = funcctx->attinmeta;-- if (call_cntr < max_calls) /* do when there is more left to send */+ if (funcctx->call_cntr < funcctx->max_calls) /* do when there is more left to send */
{
- char **values;+ Datum values[5];+ bool nulls[5];
HeapTuple tuple;
Datum result;
+ int dims[1];+ int lbs[1];- StringInfoData itemValues;- StringInfoData itemNulls;+ Datum *itemNulls;+ Datum *itemValues;
int i;
@@ -1203,24 +1199,16 @@ pg_stats_ext_mcvlist_items(PG_FUNCTION_ARGS)
mcvlist = (MCVList *) funcctx->user_fctx;
- Assert(call_cntr < mcvlist->nitems);-- item = &mcvlist->items[call_cntr];-- /*- * Prepare a values array for building the returned tuple. This should- * be an array of C strings which will be processed later by the type- * input functions.- */- values = (char **) palloc0(5 * sizeof(char *));+ Assert(funcctx->call_cntr < mcvlist->nitems);- values[0] = (char *) palloc(64 * sizeof(char)); /* item index */- values[3] = (char *) palloc(64 * sizeof(char)); /* frequency */- values[4] = (char *) palloc(64 * sizeof(char)); /* base frequency */+ item = &mcvlist->items[funcctx->call_cntr];
outfuncs = (Oid *) palloc0(sizeof(Oid) * mcvlist->ndimensions);
fmgrinfo = (FmgrInfo *) palloc0(sizeof(FmgrInfo) * mcvlist->ndimensions);
+ itemValues = (Datum *) palloc(sizeof(Datum) * mcvlist->ndimensions);+ itemNulls = (Datum *) palloc(sizeof(Datum) * mcvlist->ndimensions);+
for (i = 0; i < mcvlist->ndimensions; i++)
{
bool isvarlena;
@@ -1230,61 +1218,49 @@ pg_stats_ext_mcvlist_items(PG_FUNCTION_ARGS)
fmgr_info(outfuncs[i], &fmgrinfo[i]);
}
- /* build the arrays of values / nulls */- initStringInfo(&itemValues);- initStringInfo(&itemNulls);-- appendStringInfoChar(&itemValues, '{');- appendStringInfoChar(&itemNulls, '{');-
for (i = 0; i < mcvlist->ndimensions; i++)
{
- Datum val,- valout;-- if (i > 0)- {- appendStringInfoString(&itemValues, ", ");- appendStringInfoString(&itemNulls, ", ");- }+ Datum valout;
if (item->isnull[i])
- valout = CStringGetDatum("NULL");+ valout = (Datum) 0;
else
- {- val = item->values[i];- valout = FunctionCall1(&fmgrinfo[i], val);- }+ valout = FunctionCall1(&fmgrinfo[i], item->values[i]);- appendStringInfoString(&itemValues, DatumGetCString(valout));- appendStringInfoString(&itemNulls, item->isnull[i] ? "t" : "f");+ itemNulls[i] = BoolGetDatum(item->isnull[i]);+ itemValues[i] = valout;
}
- appendStringInfoChar(&itemValues, '}');- appendStringInfoChar(&itemNulls, '}');+ dims[0] = mcvlist->ndimensions;+ lbs[0] = 1;++ values[0] = Int32GetDatum(funcctx->call_cntr);- snprintf(values[0], 64, "%d", call_cntr);- snprintf(values[3], 64, "%f", item->frequency);- snprintf(values[4], 64, "%f", item->base_frequency);+ values[1] = PointerGetDatum(construct_md_array(itemValues,+ item->isnull,+ 1,+ dims,+ lbs,+ CSTRINGOID, -2,+ false, 'c'));- values[1] = itemValues.data;- values[2] = itemNulls.data;+ values[2] = PointerGetDatum(construct_array(itemNulls,+ mcvlist->ndimensions,+ BOOLOID, sizeof(bool),+ true, 'c'));++ values[3] = Float8GetDatum(item->frequency);+ values[4] = Float8GetDatum(item->base_frequency);++ /* no NULLs in the tuple */+ memset(nulls, 0, sizeof(nulls));
/* build a tuple */
- tuple = BuildTupleFromCStrings(attinmeta, values);+ tuple = heap_form_tuple(funcctx->attinmeta->tupdesc, values, nulls);
/* make the tuple into a datum */
result = HeapTupleGetDatum(tuple);
- /* clean up (this is not really necessary) */- pfree(itemValues.data);- pfree(itemNulls.data);-- pfree(values[0]);- pfree(values[3]);- pfree(values[4]);- pfree(values);-
SRF_RETURN_NEXT(funcctx, result);
}
else /* do when there is no more left */
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.datindex 87335248a0..36ae2ac9d8 100644--- a/src/include/catalog/pg_proc.dat+++ b/src/include/catalog/pg_proc.dat@@ -5019,7 +5019,7 @@
{ oid => '3427', descr => 'details about MCV list items',
proname => 'pg_mcv_list_items', prorows => '1000', proretset => 't',
provolatile => 's', prorettype => 'record', proargtypes => 'pg_mcv_list',
- proallargtypes => '{pg_mcv_list,int4,text,_bool,float8,float8}',+ proallargtypes => '{pg_mcv_list,int4,_text,_bool,float8,float8}',
proargmodes => '{i,o,o,o,o,o}',
proargnames => '{mcv_list,index,values,nulls,frequency,base_frequency}',
prosrc => 'pg_stats_ext_mcvlist_items' },
--
2.20.1
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To: pgsql-hackers@postgresql.org
Cc: tomas.vondra@2ndquadrant.com, dean.a.rasheed@gmail.com, pgsql-hackers@lists.postgresql.org
Subject: Re: Choosing values for multivariate MCV lists
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