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contrib/tsm_system_rows
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‎contrib/tsm_system_rows/.gitignore

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# Generated subdirectories
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/log/
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/results/
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/tmp_check/

‎contrib/tsm_system_rows/Makefile

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# src/test/modules/tsm_system_rows/Makefile
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MODULE_big = tsm_system_rows
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OBJS = tsm_system_rows.o $(WIN32RES)
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PGFILEDESC = "tsm_system_rows - SYSTEM TABLESAMPLE method which accepts number of rows as a limit"
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EXTENSION = tsm_system_rows
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DATA = tsm_system_rows--1.0.sql
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REGRESS = tsm_system_rows
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ifdef USE_PGXS
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PG_CONFIG = pg_config
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PGXS := $(shell $(PG_CONFIG) --pgxs)
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include $(PGXS)
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else
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subdir = contrib/tsm_system_rows
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top_builddir = ../..
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include $(top_builddir)/src/Makefile.global
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include $(top_srcdir)/contrib/contrib-global.mk
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endif

‎contrib/tsm_system_rows/expected/tsm_system_rows.out

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CREATE EXTENSION tsm_system_rows;
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CREATE TABLE test_tablesample (id int, name text) WITH (fillfactor=10); -- force smaller pages so we don't have to load too much data to get multiple pages
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INSERT INTO test_tablesample SELECT i, repeat(i::text, 1000) FROM generate_series(0, 30) s(i) ORDER BY i;
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ANALYZE test_tablesample;
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SELECT count(*) FROM test_tablesample TABLESAMPLE system_rows (1000);
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count
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-------
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31
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(1 row)
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SELECT id FROM test_tablesample TABLESAMPLE system_rows (8) REPEATABLE (5432);
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id
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----
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7
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14
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21
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28
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4
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11
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18
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25
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(8 rows)
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EXPLAIN SELECT id FROM test_tablesample TABLESAMPLE system_rows (20) REPEATABLE (10);
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QUERY PLAN
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-----------------------------------------------------------------------------------
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Sample Scan (system_rows) on test_tablesample (cost=0.00..80.20 rows=20 width=4)
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(1 row)
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-- done
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DROP TABLE test_tablesample CASCADE;

‎contrib/tsm_system_rows/sql/tsm_system_rows.sql

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CREATE EXTENSION tsm_system_rows;
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CREATE TABLE test_tablesample (id int, name text) WITH (fillfactor=10); -- force smaller pages so we don't have to load too much data to get multiple pages
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INSERT INTO test_tablesample SELECT i, repeat(i::text, 1000) FROM generate_series(0, 30) s(i) ORDER BY i;
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ANALYZE test_tablesample;
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SELECT count(*) FROM test_tablesample TABLESAMPLE system_rows (1000);
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SELECT id FROM test_tablesample TABLESAMPLE system_rows (8) REPEATABLE (5432);
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EXPLAIN SELECT id FROM test_tablesample TABLESAMPLE system_rows (20) REPEATABLE (10);
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-- done
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DROP TABLE test_tablesample CASCADE;

‎contrib/tsm_system_rows/tsm_system_rows--1.0.sql

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/* src/test/modules/tablesample/tsm_system_rows--1.0.sql */
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-- complain if script is sourced in psql, rather than via CREATE EXTENSION
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\echo Use "CREATE EXTENSION tsm_system_rows" to load this file. \quit
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CREATE FUNCTION tsm_system_rows_init(internal, int4, int4)
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RETURNS void
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AS 'MODULE_PATHNAME'
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LANGUAGE C STRICT;
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CREATE FUNCTION tsm_system_rows_nextblock(internal)
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RETURNS int4
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AS 'MODULE_PATHNAME'
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LANGUAGE C STRICT;
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CREATE FUNCTION tsm_system_rows_nexttuple(internal, int4, int2)
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RETURNS int2
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AS 'MODULE_PATHNAME'
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LANGUAGE C STRICT;
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CREATE FUNCTION tsm_system_rows_examinetuple(internal, int4, internal, bool)
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RETURNS bool
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AS 'MODULE_PATHNAME'
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LANGUAGE C STRICT;
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CREATE FUNCTION tsm_system_rows_end(internal)
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RETURNS void
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AS 'MODULE_PATHNAME'
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LANGUAGE C STRICT;
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CREATE FUNCTION tsm_system_rows_reset(internal)
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RETURNS void
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AS 'MODULE_PATHNAME'
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LANGUAGE C STRICT;
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CREATE FUNCTION tsm_system_rows_cost(internal, internal, internal, internal, internal, internal, internal)
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RETURNS void
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AS 'MODULE_PATHNAME'
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LANGUAGE C STRICT;
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INSERT INTO pg_tablesample_method VALUES('system_rows', false, true,
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'tsm_system_rows_init', 'tsm_system_rows_nextblock',
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'tsm_system_rows_nexttuple', 'tsm_system_rows_examinetuple',
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'tsm_system_rows_end', 'tsm_system_rows_reset', 'tsm_system_rows_cost');
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‎contrib/tsm_system_rows/tsm_system_rows.c

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/*-------------------------------------------------------------------------
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*
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* tsm_system_rows.c
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* interface routines for system_rows tablesample method
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*
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*
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* Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* contrib/tsm_system_rows_rowlimit/tsm_system_rows.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 "fmgr.h"
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#include "access/tablesample.h"
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#include "access/relscan.h"
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#include "miscadmin.h"
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#include "nodes/execnodes.h"
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#include "nodes/relation.h"
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#include "optimizer/clauses.h"
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#include "storage/bufmgr.h"
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#include "utils/sampling.h"
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PG_MODULE_MAGIC;
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/*
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* State
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*/
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typedef struct
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{
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SamplerRandomState randstate;
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uint32 seed; /* random seed */
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BlockNumber nblocks; /* number of block in relation */
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int32 ntuples; /* number of tuples to return */
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int32 donetuples; /* tuples already returned */
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OffsetNumber lt; /* last tuple returned from current block */
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BlockNumber step; /* step size */
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BlockNumber lb; /* last block visited */
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BlockNumber doneblocks; /* number of already returned blocks */
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} SystemSamplerData;
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PG_FUNCTION_INFO_V1(tsm_system_rows_init);
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PG_FUNCTION_INFO_V1(tsm_system_rows_nextblock);
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PG_FUNCTION_INFO_V1(tsm_system_rows_nexttuple);
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PG_FUNCTION_INFO_V1(tsm_system_rows_examinetuple);
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PG_FUNCTION_INFO_V1(tsm_system_rows_end);
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PG_FUNCTION_INFO_V1(tsm_system_rows_reset);
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PG_FUNCTION_INFO_V1(tsm_system_rows_cost);
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static uint32 random_relative_prime(uint32 n, SamplerRandomState randstate);
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/*
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* Initializes the state.
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*/
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Datum
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tsm_system_rows_init(PG_FUNCTION_ARGS)
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{
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TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
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uint32 seed = PG_GETARG_UINT32(1);
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int32 ntuples = PG_ARGISNULL(2) ? -1 : PG_GETARG_INT32(2);
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HeapScanDesc scan = tsdesc->heapScan;
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SystemSamplerData *sampler;
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if (ntuples < 1)
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ereport(ERROR,
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(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
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errmsg("invalid sample size"),
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errhint("Sample size must be positive integer value.")));
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sampler = palloc0(sizeof(SystemSamplerData));
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/* Remember initial values for reinit */
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sampler->seed = seed;
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sampler->nblocks = scan->rs_nblocks;
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sampler->ntuples = ntuples;
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sampler->donetuples = 0;
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sampler->lt = InvalidOffsetNumber;
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sampler->doneblocks = 0;
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sampler_random_init_state(sampler->seed, sampler->randstate);
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/* Find relative prime as step size for linear probing. */
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sampler->step = random_relative_prime(sampler->nblocks, sampler->randstate);
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/*
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* Randomize start position so that blocks close to step size don't have
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* higher probability of being chosen on very short scan.
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*/
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sampler->lb = sampler_random_fract(sampler->randstate) *
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(sampler->nblocks / sampler->step);
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tsdesc->tsmdata = (void *) sampler;
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PG_RETURN_VOID();
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}
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/*
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* Get next block number or InvalidBlockNumber when we're done.
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*
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* Uses linear probing algorithm for picking next block.
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*/
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Datum
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tsm_system_rows_nextblock(PG_FUNCTION_ARGS)
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{
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TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
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SystemSamplerData *sampler = (SystemSamplerData *) tsdesc->tsmdata;
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sampler->lb = (sampler->lb + sampler->step) % sampler->nblocks;
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sampler->doneblocks++;
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/* All blocks have been read, we're done */
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if (sampler->doneblocks > sampler->nblocks ||
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sampler->donetuples >= sampler->ntuples)
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PG_RETURN_UINT32(InvalidBlockNumber);
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PG_RETURN_UINT32(sampler->lb);
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}
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/*
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* Get next tuple offset in current block or InvalidOffsetNumber if we are done
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* with this block.
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*/
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Datum
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tsm_system_rows_nexttuple(PG_FUNCTION_ARGS)
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{
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TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
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OffsetNumber maxoffset = PG_GETARG_UINT16(2);
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SystemSamplerData *sampler = (SystemSamplerData *) tsdesc->tsmdata;
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OffsetNumber tupoffset = sampler->lt;
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if (tupoffset == InvalidOffsetNumber)
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tupoffset = FirstOffsetNumber;
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else
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tupoffset++;
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if (tupoffset > maxoffset ||
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sampler->donetuples >= sampler->ntuples)
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tupoffset = InvalidOffsetNumber;
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sampler->lt = tupoffset;
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PG_RETURN_UINT16(tupoffset);
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}
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/*
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* Examine tuple and decide if it should be returned.
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*/
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Datum
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tsm_system_rows_examinetuple(PG_FUNCTION_ARGS)
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{
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TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
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bool visible = PG_GETARG_BOOL(3);
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SystemSamplerData *sampler = (SystemSamplerData *) tsdesc->tsmdata;
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if (!visible)
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PG_RETURN_BOOL(false);
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sampler->donetuples++;
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PG_RETURN_BOOL(true);
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}
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/*
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* Cleanup method.
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*/
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Datum
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tsm_system_rows_end(PG_FUNCTION_ARGS)
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{
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TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
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pfree(tsdesc->tsmdata);
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PG_RETURN_VOID();
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}
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/*
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* Reset state (called by ReScan).
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*/
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Datum
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tsm_system_rows_reset(PG_FUNCTION_ARGS)
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{
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TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
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SystemSamplerData *sampler = (SystemSamplerData *) tsdesc->tsmdata;
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sampler->lt = InvalidOffsetNumber;
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sampler->donetuples = 0;
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sampler->doneblocks = 0;
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sampler_random_init_state(sampler->seed, sampler->randstate);
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sampler->step = random_relative_prime(sampler->nblocks, sampler->randstate);
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sampler->lb = sampler_random_fract(sampler->randstate) * (sampler->nblocks / sampler->step);
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PG_RETURN_VOID();
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}
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/*
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* Costing function.
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*/
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Datum
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tsm_system_rows_cost(PG_FUNCTION_ARGS)
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{
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PlannerInfo *root = (PlannerInfo *) PG_GETARG_POINTER(0);
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Path *path = (Path *) PG_GETARG_POINTER(1);
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RelOptInfo *baserel = (RelOptInfo *) PG_GETARG_POINTER(2);
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List *args = (List *) PG_GETARG_POINTER(3);
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BlockNumber *pages = (BlockNumber *) PG_GETARG_POINTER(4);
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double *tuples = (double *) PG_GETARG_POINTER(5);
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Node *limitnode;
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int32 ntuples;
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limitnode = linitial(args);
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limitnode = estimate_expression_value(root, limitnode);
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if (IsA(limitnode, RelabelType))
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limitnode = (Node *) ((RelabelType *) limitnode)->arg;
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if (IsA(limitnode, Const))
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ntuples = DatumGetInt32(((Const *) limitnode)->constvalue);
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else
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{
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/* Default ntuples if the estimation didn't return Const. */
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ntuples = 1000;
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}
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*pages = Min(baserel->pages, ntuples);
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*tuples = ntuples;
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path->rows = *tuples;
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PG_RETURN_VOID();
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}
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static uint32
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gcd (uint32 a, uint32 b)
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{
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uint32 c;
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while (a != 0)
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{
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c = a;
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a = b % a;
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b = c;
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}
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return b;
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}
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static uint32
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random_relative_prime(uint32 n, SamplerRandomState randstate)
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{
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/* Pick random starting number, with some limits on what it can be. */
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uint32 r = (uint32) sampler_random_fract(randstate) * n/2 + n/4,
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t;
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/*
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* This should only take 2 or 3 iterations as the probability of 2 numbers
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* being relatively prime is ~61%.
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*/
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while ((t = gcd(r, n)) > 1)
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{
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CHECK_FOR_INTERRUPTS();
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r /= t;
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}
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return r;
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}

‎contrib/tsm_system_rows/tsm_system_rows.control

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# tsm_system_rows extension
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comment = 'SYSTEM TABLESAMPLE method which accepts number rows as a limit'
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default_version = '1.0'
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module_pathname = '$libdir/tsm_system_rows'
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relocatable = true

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