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/*-------------------------------------------------------------------------
*
* system.c
* interface routines for system tablesample method
*
*
* Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
*
* IDENTIFICATION
* src/backend/utils/tablesample/system.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "fmgr.h"
#include "access/tablesample.h"
#include "access/relscan.h"
#include "nodes/execnodes.h"
#include "nodes/relation.h"
#include "optimizer/clauses.h"
#include "storage/bufmgr.h"
#include "utils/sampling.h"
/*
* State
*/
typedef struct
{
BlockSamplerData bs;
uint32 seed; /* random seed */
BlockNumber nblocks; /* number of block in relation */
int samplesize; /* number of blocks to return */
OffsetNumber lt; /* last tuple returned from current block */
} SystemSamplerData;
/*
* Initializes the state.
*/
Datum
tsm_system_init(PG_FUNCTION_ARGS)
{
TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
uint32 seed = PG_GETARG_UINT32(1);
float4 percent = PG_ARGISNULL(2) ? -1 : PG_GETARG_FLOAT4(2);
HeapScanDesc scan = tsdesc->heapScan;
SystemSamplerData *sampler;
if (percent < 0 || percent > 100)
ereport(ERROR,
(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
errmsg("invalid sample size"),
errhint("Sample size must be numeric value between 0 and 100 (inclusive).")));
sampler = palloc0(sizeof(SystemSamplerData));
/* Remember initial values for reinit */
sampler->seed = seed;
sampler->nblocks = scan->rs_nblocks;
sampler->samplesize = 1 + (int) (sampler->nblocks * (percent / 100.0));
sampler->lt = InvalidOffsetNumber;
BlockSampler_Init(&sampler->bs, sampler->nblocks, sampler->samplesize,
sampler->seed);
tsdesc->tsmdata = (void *) sampler;
PG_RETURN_VOID();
}
/*
* Get next block number or InvalidBlockNumber when we're done.
*
* Uses the same logic as ANALYZE for picking the random blocks.
*/
Datum
tsm_system_nextblock(PG_FUNCTION_ARGS)
{
TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
SystemSamplerData *sampler = (SystemSamplerData *) tsdesc->tsmdata;
BlockNumber blockno;
if (!BlockSampler_HasMore(&sampler->bs))
PG_RETURN_UINT32(InvalidBlockNumber);
blockno = BlockSampler_Next(&sampler->bs);
PG_RETURN_UINT32(blockno);
}
/*
* Get next tuple offset in current block or InvalidOffsetNumber if we are done
* with this block.
*/
Datum
tsm_system_nexttuple(PG_FUNCTION_ARGS)
{
TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
OffsetNumber maxoffset = PG_GETARG_UINT16(2);
SystemSamplerData *sampler = (SystemSamplerData *) tsdesc->tsmdata;
OffsetNumber tupoffset = sampler->lt;
if (tupoffset == InvalidOffsetNumber)
tupoffset = FirstOffsetNumber;
else
tupoffset++;
if (tupoffset > maxoffset)
tupoffset = InvalidOffsetNumber;
sampler->lt = tupoffset;
PG_RETURN_UINT16(tupoffset);
}
/*
* Cleanup method.
*/
Datum
tsm_system_end(PG_FUNCTION_ARGS)
{
TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
pfree(tsdesc->tsmdata);
PG_RETURN_VOID();
}
/*
* Reset state (called by ReScan).
*/
Datum
tsm_system_reset(PG_FUNCTION_ARGS)
{
TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
SystemSamplerData *sampler = (SystemSamplerData *) tsdesc->tsmdata;
sampler->lt = InvalidOffsetNumber;
BlockSampler_Init(&sampler->bs, sampler->nblocks, sampler->samplesize,
sampler->seed);
PG_RETURN_VOID();
}
/*
* Costing function.
*/
Datum
tsm_system_cost(PG_FUNCTION_ARGS)
{
PlannerInfo *root = (PlannerInfo *) PG_GETARG_POINTER(0);
Path *path = (Path *) PG_GETARG_POINTER(1);
RelOptInfo *baserel = (RelOptInfo *) PG_GETARG_POINTER(2);
List *args = (List *) PG_GETARG_POINTER(3);
BlockNumber *pages = (BlockNumber *) PG_GETARG_POINTER(4);
double *tuples = (double *) PG_GETARG_POINTER(5);
Node *pctnode;
float4 samplesize;
pctnode = linitial(args);
pctnode = estimate_expression_value(root, pctnode);
if (IsA(pctnode, RelabelType))
pctnode = (Node *) ((RelabelType *) pctnode)->arg;
if (IsA(pctnode, Const))
{
samplesize = DatumGetFloat4(((Const *) pctnode)->constvalue);
samplesize /= 100.0;
}
else
{
/* Default samplesize if the estimation didn't return Const. */
samplesize = 0.1f;
}
*pages = baserel->pages * samplesize;
*tuples = path->rows * samplesize;
path->rows = *tuples;
PG_RETURN_VOID();
}
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