rueian

package main

import (
	"crypto/rand"
	"database/sql"
	_ "github.com/lib/pq"
	"time"
)

const (

rueian

package main

import (
	"encoding/hex"
	"fmt"
	"github.com/rueian/pgbroker/backend"
	"github.com/rueian/pgbroker/message"
	"github.com/rueian/pgbroker/proxy"
	"net"
)

rueian

postgres=# explain analyze select * from counters where id like 'ms:149895:%';
                                                        QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------
 Index Scan using counters_pkey on counters  (cost=0.56..8.58 rows=49 width=36) (actual time=0.015..0.023 rows=10 loops=1)
   Index Cond: ((id >= 'ms:149895:'::text) AND (id < 'ms:149895;'::text))
   Filter: (id ~~ 'ms:149895:%'::text)
 Planning Time: 0.146 ms
 Execution Time: 0.036 ms
(5 rows)

rueian

		/* In any case, don't believe extremely small or large estimates. */
		if (selec < 0.00001)
			selec = 0.00001;
		else if (selec > 0.9999)
			selec = 0.9999;

rueian

	else if (IsA(rawreq, SupportRequestIndexCondition))
	{
		/* Try to convert operator/function call to index conditions */
		SupportRequestIndexCondition *req = (SupportRequestIndexCondition *) rawreq;

		/*
		 * Currently we have no "reverse" match operators with the pattern on
		 * the left, so we only need consider cases with the indexkey on the
		 * left.
		 */

rueian

postgres=# explain analyze select * from counters where id >= 'ms:149895:' and id <= 'ms:149895;' and id like 'ms:149895:%';
 QUERY PLAN
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
 Index Scan using counters_pkey on counters (cost=0.56..8.58 rows=1 width=36) (actual time=0.023..0.039 rows=10 loops=1)
 Index Cond: ((id >= 'ms:149895:'::text) AND (id <= 'ms:149895;'::text) AND (id >= 'ms:149895:'::text) AND (id < 'ms:149895;'::text))
 Filter: (id ~~ 'ms:149895:%'::text)
 Planning Time: 0.156 ms
 Execution Time: 0.036 ms
(5 rows)

rueian

postgres=# EXPLAIN SELECT * FROM counters;
 QUERY PLAN
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Seq Scan on counters (cost=0.00..89169.11 rows=4880311 width=36)
(1 row)

rueian

postgres=# SELECT unnest(histogram_bounds::text::text[]) FROM pg_stats WHERE tablename='counters' AND attname='id';
 unnest
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
 ms:103734:p
 ms:1074631:cl
 ms:1103301:c
 ms:1137423:pn
 ms:1168158:pr
 ms:1192862:p
 ms:1221019:cl

rueian

postgres=# SELECT array_length(histogram_bounds, 1) FROM pg_stats WHERE tablename='counters' AND attname='id';
 array_length
 - - - - - - - 
 101
(1 row)

rueian

		/*
		 * If we have most-common-values info, add up the fractions of the MCV
		 * entries that satisfy MCV OP PATTERN.  These fractions contribute
		 * directly to the result selectivity.  Also add up the total fraction
		 * represented by MCV entries.
		 */
		mcv_selec = mcv_selectivity(&vardata, &opproc, constval, true,
									&sumcommon);

		/*