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9aab83fc50
The mess cleaned up in commit da0759600 is clear evidence that it's a
bug hazard to expect the caller of get_attstatsslot()/free_attstatsslot()
to provide the correct type OID for the array elements in the slot.
Moreover, we weren't even getting any performance benefit from that,
since get_attstatsslot() was extracting the real type OID from the array
anyway. So we ought to get rid of that requirement; indeed, it would
make more sense for get_attstatsslot() to pass back the type OID it found,
in case the caller isn't sure what to expect, which is likely in binary-
compatible-operator cases.
Another problem with the current implementation is that if the stats array
element type is pass-by-reference, we incur a palloc/memcpy/pfree cycle
for each element. That seemed acceptable when the code was written because
we were targeting O(10) array sizes --- but these days, stats arrays are
almost always bigger than that, sometimes much bigger. We can save a
significant number of cycles by doing one palloc/memcpy/pfree of the whole
array. Indeed, in the now-probably-common case where the array is toasted,
that happens anyway so this method is basically free. (Note: although the
catcache code will inline any out-of-line toasted values, it doesn't
decompress them. At the other end of the size range, it doesn't expand
short-header datums either. In either case, DatumGetArrayTypeP would have
to make a copy. We do end up using an extra array copy step if the element
type is pass-by-value and the array length is neither small enough for a
short header nor large enough to have suffered compression. But that
seems like a very acceptable price for winning in pass-by-ref cases.)
Hence, redesign to take these insights into account. While at it,
convert to an API in which we fill a struct rather than passing a bunch
of pointers to individual output arguments. That will make it less
painful if we ever want further expansion of what get_attstatsslot can
pass back.
It's certainly arguable that this is new development and not something to
push post-feature-freeze. However, I view it as primarily bug-proofing
and therefore something that's better to have sooner not later. Since
we aren't quite at beta phase yet, let's put it in.
Discussion: https://postgr.es/m/16364.1494520862@sss.pgh.pa.us
334 lines
8.5 KiB
C
334 lines
8.5 KiB
C
/*-------------------------------------------------------------------------
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*
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* _int_selfuncs.c
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* Functions for selectivity estimation of intarray operators
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*
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* Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* contrib/intarray/_int_selfuncs.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "_int.h"
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#include "access/htup_details.h"
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#include "catalog/pg_operator.h"
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#include "catalog/pg_statistic.h"
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#include "catalog/pg_type.h"
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#include "utils/builtins.h"
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#include "utils/selfuncs.h"
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#include "utils/syscache.h"
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#include "utils/lsyscache.h"
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#include "miscadmin.h"
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PG_FUNCTION_INFO_V1(_int_overlap_sel);
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PG_FUNCTION_INFO_V1(_int_contains_sel);
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PG_FUNCTION_INFO_V1(_int_contained_sel);
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PG_FUNCTION_INFO_V1(_int_overlap_joinsel);
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PG_FUNCTION_INFO_V1(_int_contains_joinsel);
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PG_FUNCTION_INFO_V1(_int_contained_joinsel);
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PG_FUNCTION_INFO_V1(_int_matchsel);
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static Selectivity int_query_opr_selec(ITEM *item, Datum *values, float4 *freqs,
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int nmncelems, float4 minfreq);
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static int compare_val_int4(const void *a, const void *b);
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/*
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* Wrappers around the default array selectivity estimation functions.
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*
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* The default array selectivity operators for the @>, && and @< operators
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* work fine for integer arrays. However, if we tried to just use arraycontsel
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* and arracontjoinsel directly as the cost estimator functions for our
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* operators, they would not work as intended, because they look at the
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* operator's OID. Our operators behave exactly like the built-in anyarray
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* versions, but we must tell the cost estimator functions which built-in
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* operators they correspond to. These wrappers just replace the operator
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* OID with the corresponding built-in operator's OID, and call the built-in
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* function.
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*/
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Datum
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_int_overlap_sel(PG_FUNCTION_ARGS)
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{
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PG_RETURN_DATUM(DirectFunctionCall4(arraycontsel,
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PG_GETARG_DATUM(0),
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ObjectIdGetDatum(OID_ARRAY_OVERLAP_OP),
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PG_GETARG_DATUM(2),
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PG_GETARG_DATUM(3)));
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}
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Datum
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_int_contains_sel(PG_FUNCTION_ARGS)
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{
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PG_RETURN_DATUM(DirectFunctionCall4(arraycontsel,
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PG_GETARG_DATUM(0),
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ObjectIdGetDatum(OID_ARRAY_CONTAINS_OP),
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PG_GETARG_DATUM(2),
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PG_GETARG_DATUM(3)));
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}
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Datum
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_int_contained_sel(PG_FUNCTION_ARGS)
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{
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PG_RETURN_DATUM(DirectFunctionCall4(arraycontsel,
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PG_GETARG_DATUM(0),
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ObjectIdGetDatum(OID_ARRAY_CONTAINED_OP),
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PG_GETARG_DATUM(2),
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PG_GETARG_DATUM(3)));
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}
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Datum
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_int_overlap_joinsel(PG_FUNCTION_ARGS)
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{
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PG_RETURN_DATUM(DirectFunctionCall5(arraycontjoinsel,
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PG_GETARG_DATUM(0),
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ObjectIdGetDatum(OID_ARRAY_OVERLAP_OP),
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PG_GETARG_DATUM(2),
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PG_GETARG_DATUM(3),
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PG_GETARG_DATUM(4)));
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}
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Datum
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_int_contains_joinsel(PG_FUNCTION_ARGS)
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{
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PG_RETURN_DATUM(DirectFunctionCall5(arraycontjoinsel,
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PG_GETARG_DATUM(0),
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ObjectIdGetDatum(OID_ARRAY_CONTAINS_OP),
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PG_GETARG_DATUM(2),
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PG_GETARG_DATUM(3),
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PG_GETARG_DATUM(4)));
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}
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Datum
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_int_contained_joinsel(PG_FUNCTION_ARGS)
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{
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PG_RETURN_DATUM(DirectFunctionCall5(arraycontjoinsel,
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PG_GETARG_DATUM(0),
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ObjectIdGetDatum(OID_ARRAY_CONTAINED_OP),
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PG_GETARG_DATUM(2),
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PG_GETARG_DATUM(3),
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PG_GETARG_DATUM(4)));
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}
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/*
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* _int_matchsel -- restriction selectivity function for intarray @@ query_int
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*/
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Datum
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_int_matchsel(PG_FUNCTION_ARGS)
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{
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PlannerInfo *root = (PlannerInfo *) PG_GETARG_POINTER(0);
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List *args = (List *) PG_GETARG_POINTER(2);
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int varRelid = PG_GETARG_INT32(3);
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VariableStatData vardata;
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Node *other;
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bool varonleft;
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Selectivity selec;
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QUERYTYPE *query;
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Datum *mcelems = NULL;
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float4 *mcefreqs = NULL;
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int nmcelems = 0;
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float4 minfreq = 0.0;
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float4 nullfrac = 0.0;
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AttStatsSlot sslot;
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/*
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* If expression is not "variable @@ something" or "something @@ variable"
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* then punt and return a default estimate.
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*/
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if (!get_restriction_variable(root, args, varRelid,
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&vardata, &other, &varonleft))
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PG_RETURN_FLOAT8(DEFAULT_EQ_SEL);
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/*
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* Variable should be int[]. We don't support cases where variable is
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* query_int.
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*/
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if (vardata.vartype != INT4ARRAYOID)
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PG_RETURN_FLOAT8(DEFAULT_EQ_SEL);
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/*
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* Can't do anything useful if the something is not a constant, either.
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*/
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if (!IsA(other, Const))
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{
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ReleaseVariableStats(vardata);
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PG_RETURN_FLOAT8(DEFAULT_EQ_SEL);
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}
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/*
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* The "@@" operator is strict, so we can cope with NULL right away.
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*/
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if (((Const *) other)->constisnull)
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{
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ReleaseVariableStats(vardata);
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PG_RETURN_FLOAT8(0.0);
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}
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/* The caller made sure the const is a query, so get it now */
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query = DatumGetQueryTypeP(((Const *) other)->constvalue);
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/* Empty query matches nothing */
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if (query->size == 0)
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{
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ReleaseVariableStats(vardata);
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return (Selectivity) 0.0;
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}
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/*
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* Get the statistics for the intarray column.
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*
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* We're interested in the Most-Common-Elements list, and the NULL
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* fraction.
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*/
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if (HeapTupleIsValid(vardata.statsTuple))
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{
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Form_pg_statistic stats;
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stats = (Form_pg_statistic) GETSTRUCT(vardata.statsTuple);
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nullfrac = stats->stanullfrac;
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/*
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* For an int4 array, the default array type analyze function will
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* collect a Most Common Elements list, which is an array of int4s.
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*/
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if (get_attstatsslot(&sslot, vardata.statsTuple,
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STATISTIC_KIND_MCELEM, InvalidOid,
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ATTSTATSSLOT_VALUES | ATTSTATSSLOT_NUMBERS))
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{
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Assert(sslot.valuetype == INT4OID);
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/*
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* There should be three more Numbers than Values, because the
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* last three (for intarray) cells are taken for minimal, maximal
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* and nulls frequency. Punt if not.
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*/
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if (sslot.nnumbers == sslot.nvalues + 3)
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{
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/* Grab the lowest frequency. */
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minfreq = sslot.numbers[sslot.nnumbers - (sslot.nnumbers - sslot.nvalues)];
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mcelems = sslot.values;
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mcefreqs = sslot.numbers;
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nmcelems = sslot.nvalues;
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}
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}
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}
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else
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memset(&sslot, 0, sizeof(sslot));
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/* Process the logical expression in the query, using the stats */
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selec = int_query_opr_selec(GETQUERY(query) + query->size - 1,
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mcelems, mcefreqs, nmcelems, minfreq);
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/* MCE stats count only non-null rows, so adjust for null rows. */
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selec *= (1.0 - nullfrac);
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free_attstatsslot(&sslot);
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ReleaseVariableStats(vardata);
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CLAMP_PROBABILITY(selec);
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PG_RETURN_FLOAT8((float8) selec);
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}
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/*
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* Estimate selectivity of single intquery operator
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*/
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static Selectivity
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int_query_opr_selec(ITEM *item, Datum *mcelems, float4 *mcefreqs,
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int nmcelems, float4 minfreq)
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{
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Selectivity selec;
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/* since this function recurses, it could be driven to stack overflow */
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check_stack_depth();
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if (item->type == VAL)
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{
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Datum *searchres;
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if (mcelems == NULL)
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return (Selectivity) DEFAULT_EQ_SEL;
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searchres = (Datum *) bsearch(&item->val, mcelems, nmcelems,
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sizeof(Datum), compare_val_int4);
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if (searchres)
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{
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/*
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* The element is in MCELEM. Return precise selectivity (or at
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* least as precise as ANALYZE could find out).
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*/
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selec = mcefreqs[searchres - mcelems];
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}
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else
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{
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/*
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* The element is not in MCELEM. Punt, but assume that the
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* selectivity cannot be more than minfreq / 2.
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*/
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selec = Min(DEFAULT_EQ_SEL, minfreq / 2);
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}
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}
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else if (item->type == OPR)
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{
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/* Current query node is an operator */
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Selectivity s1,
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s2;
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s1 = int_query_opr_selec(item - 1, mcelems, mcefreqs, nmcelems,
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minfreq);
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switch (item->val)
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{
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case (int32) '!':
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selec = 1.0 - s1;
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break;
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case (int32) '&':
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s2 = int_query_opr_selec(item + item->left, mcelems, mcefreqs,
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nmcelems, minfreq);
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selec = s1 * s2;
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break;
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case (int32) '|':
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s2 = int_query_opr_selec(item + item->left, mcelems, mcefreqs,
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nmcelems, minfreq);
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selec = s1 + s2 - s1 * s2;
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break;
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default:
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elog(ERROR, "unrecognized operator: %d", item->val);
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selec = 0; /* keep compiler quiet */
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break;
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}
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}
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else
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{
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elog(ERROR, "unrecognized int query item type: %u", item->type);
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selec = 0; /* keep compiler quiet */
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}
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/* Clamp intermediate results to stay sane despite roundoff error */
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CLAMP_PROBABILITY(selec);
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return selec;
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}
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/*
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* Comparison function for binary search in mcelem array.
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*/
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static int
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compare_val_int4(const void *a, const void *b)
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{
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int32 key = *(int32 *) a;
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const Datum *t = (const Datum *) b;
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return key - DatumGetInt32(*t);
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}
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