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bernoulli.c File Reference
#include "postgres.h"
#include <math.h>
#include "access/tsmapi.h"
#include "catalog/pg_type.h"
#include "common/hashfn.h"
#include "optimizer/optimizer.h"
#include "utils/fmgrprotos.h"
Include dependency graph for bernoulli.c:

Go to the source code of this file.

Data Structures

struct  BernoulliSamplerData
 

Functions

static void bernoulli_samplescangetsamplesize (PlannerInfo *root, RelOptInfo *baserel, List *paramexprs, BlockNumber *pages, double *tuples)
 
static void bernoulli_initsamplescan (SampleScanState *node, int eflags)
 
static void bernoulli_beginsamplescan (SampleScanState *node, Datum *params, int nparams, uint32 seed)
 
static OffsetNumber bernoulli_nextsampletuple (SampleScanState *node, BlockNumber blockno, OffsetNumber maxoffset)
 
Datum tsm_bernoulli_handler (PG_FUNCTION_ARGS)
 

Function Documentation

◆ bernoulli_beginsamplescan()

static void bernoulli_beginsamplescan ( SampleScanState node,
Datum params,
int  nparams,
uint32  seed 
)
static

Definition at line 136 of file bernoulli.c.

140{
142 double percent = DatumGetFloat4(params[0]);
143 double dcutoff;
144
145 if (percent < 0 || percent > 100 || isnan(percent))
147 (errcode(ERRCODE_INVALID_TABLESAMPLE_ARGUMENT),
148 errmsg("sample percentage must be between 0 and 100")));
149
150 /*
151 * The cutoff is sample probability times (PG_UINT32_MAX + 1); we have to
152 * store that as a uint64, of course. Note that this gives strictly
153 * correct behavior at the limits of zero or one probability.
154 */
155 dcutoff = rint(((double) PG_UINT32_MAX + 1) * percent / 100);
156 sampler->cutoff = (uint64) dcutoff;
157 sampler->seed = seed;
158 sampler->lt = InvalidOffsetNumber;
159
160 /*
161 * Use bulkread, since we're scanning all pages. But pagemode visibility
162 * checking is a win only at larger sampling fractions. The 25% cutoff
163 * here is based on very limited experimentation.
164 */
165 node->use_bulkread = true;
166 node->use_pagemode = (percent >= 25);
167}
#define PG_UINT32_MAX
Definition: c.h:547
uint64_t uint64
Definition: c.h:489
int errcode(int sqlerrcode)
Definition: elog.c:853
int errmsg(const char *fmt,...)
Definition: elog.c:1070
#define ERROR
Definition: elog.h:39
#define ereport(elevel,...)
Definition: elog.h:149
#define InvalidOffsetNumber
Definition: off.h:26
static float4 DatumGetFloat4(Datum X)
Definition: postgres.h:463
OffsetNumber lt
Definition: bernoulli.c:41
void * tsm_state
Definition: execnodes.h:1615

References BernoulliSamplerData::cutoff, DatumGetFloat4(), ereport, errcode(), errmsg(), ERROR, InvalidOffsetNumber, BernoulliSamplerData::lt, PG_UINT32_MAX, BernoulliSamplerData::seed, SampleScanState::tsm_state, SampleScanState::use_bulkread, and SampleScanState::use_pagemode.

Referenced by tsm_bernoulli_handler().

◆ bernoulli_initsamplescan()

static void bernoulli_initsamplescan ( SampleScanState node,
int  eflags 
)
static

Definition at line 127 of file bernoulli.c.

128{
129 node->tsm_state = palloc0(sizeof(BernoulliSamplerData));
130}
void * palloc0(Size size)
Definition: mcxt.c:1347

References palloc0(), and SampleScanState::tsm_state.

Referenced by tsm_bernoulli_handler().

◆ bernoulli_nextsampletuple()

static OffsetNumber bernoulli_nextsampletuple ( SampleScanState node,
BlockNumber  blockno,
OffsetNumber  maxoffset 
)
static

Definition at line 181 of file bernoulli.c.

184{
186 OffsetNumber tupoffset = sampler->lt;
187 uint32 hashinput[3];
188
189 /* Advance to first/next tuple in block */
190 if (tupoffset == InvalidOffsetNumber)
191 tupoffset = FirstOffsetNumber;
192 else
193 tupoffset++;
194
195 /*
196 * We compute the hash by applying hash_any to an array of 3 uint32's
197 * containing the block, offset, and seed. This is efficient to set up,
198 * and with the current implementation of hash_any, it gives
199 * machine-independent results, which is a nice property for regression
200 * testing.
201 *
202 * These words in the hash input are the same throughout the block:
203 */
204 hashinput[0] = blockno;
205 hashinput[2] = sampler->seed;
206
207 /*
208 * Loop over tuple offsets until finding suitable TID or reaching end of
209 * block.
210 */
211 for (; tupoffset <= maxoffset; tupoffset++)
212 {
213 uint32 hash;
214
215 hashinput[1] = tupoffset;
216
217 hash = DatumGetUInt32(hash_any((const unsigned char *) hashinput,
218 (int) sizeof(hashinput)));
219 if (hash < sampler->cutoff)
220 break;
221 }
222
223 if (tupoffset > maxoffset)
224 tupoffset = InvalidOffsetNumber;
225
226 sampler->lt = tupoffset;
227
228 return tupoffset;
229}
uint32_t uint32
Definition: c.h:488
static Datum hash_any(const unsigned char *k, int keylen)
Definition: hashfn.h:31
if(TABLE==NULL||TABLE_index==NULL)
Definition: isn.c:76
uint16 OffsetNumber
Definition: off.h:24
#define FirstOffsetNumber
Definition: off.h:27
static uint32 DatumGetUInt32(Datum X)
Definition: postgres.h:227
static unsigned hash(unsigned *uv, int n)
Definition: rege_dfa.c:715

References DatumGetUInt32(), FirstOffsetNumber, hash(), hash_any(), if(), InvalidOffsetNumber, BernoulliSamplerData::lt, BernoulliSamplerData::seed, and SampleScanState::tsm_state.

Referenced by tsm_bernoulli_handler().

◆ bernoulli_samplescangetsamplesize()

static void bernoulli_samplescangetsamplesize ( PlannerInfo root,
RelOptInfo baserel,
List paramexprs,
BlockNumber pages,
double *  tuples 
)
static

Definition at line 86 of file bernoulli.c.

91{
92 Node *pctnode;
93 float4 samplefract;
94
95 /* Try to extract an estimate for the sample percentage */
96 pctnode = (Node *) linitial(paramexprs);
97 pctnode = estimate_expression_value(root, pctnode);
98
99 if (IsA(pctnode, Const) &&
100 !((Const *) pctnode)->constisnull)
101 {
102 samplefract = DatumGetFloat4(((Const *) pctnode)->constvalue);
103 if (samplefract >= 0 && samplefract <= 100 && !isnan(samplefract))
104 samplefract /= 100.0f;
105 else
106 {
107 /* Default samplefract if the value is bogus */
108 samplefract = 0.1f;
109 }
110 }
111 else
112 {
113 /* Default samplefract if we didn't obtain a non-null Const */
114 samplefract = 0.1f;
115 }
116
117 /* We'll visit all pages of the baserel */
118 *pages = baserel->pages;
119
120 *tuples = clamp_row_est(baserel->tuples * samplefract);
121}
float float4
Definition: c.h:586
Node * estimate_expression_value(PlannerInfo *root, Node *node)
Definition: clauses.c:2395
double clamp_row_est(double nrows)
Definition: costsize.c:213
#define IsA(nodeptr, _type_)
Definition: nodes.h:158
#define linitial(l)
Definition: pg_list.h:178
tree ctl root
Definition: radixtree.h:1857
Definition: nodes.h:129
Cardinality tuples
Definition: pathnodes.h:949
BlockNumber pages
Definition: pathnodes.h:948

References clamp_row_est(), DatumGetFloat4(), estimate_expression_value(), IsA, linitial, RelOptInfo::pages, root, and RelOptInfo::tuples.

Referenced by tsm_bernoulli_handler().

◆ tsm_bernoulli_handler()

Datum tsm_bernoulli_handler ( PG_FUNCTION_ARGS  )

Definition at line 65 of file bernoulli.c.

66{
68
69 tsm->parameterTypes = list_make1_oid(FLOAT4OID);
70 tsm->repeatable_across_queries = true;
71 tsm->repeatable_across_scans = true;
75 tsm->NextSampleBlock = NULL;
77 tsm->EndSampleScan = NULL;
78
80}
static void bernoulli_samplescangetsamplesize(PlannerInfo *root, RelOptInfo *baserel, List *paramexprs, BlockNumber *pages, double *tuples)
Definition: bernoulli.c:86
static void bernoulli_initsamplescan(SampleScanState *node, int eflags)
Definition: bernoulli.c:127
static void bernoulli_beginsamplescan(SampleScanState *node, Datum *params, int nparams, uint32 seed)
Definition: bernoulli.c:136
static OffsetNumber bernoulli_nextsampletuple(SampleScanState *node, BlockNumber blockno, OffsetNumber maxoffset)
Definition: bernoulli.c:181
#define PG_RETURN_POINTER(x)
Definition: fmgr.h:361
#define makeNode(_type_)
Definition: nodes.h:155
#define list_make1_oid(x1)
Definition: pg_list.h:242
NextSampleTuple_function NextSampleTuple
Definition: tsmapi.h:74
bool repeatable_across_scans
Definition: tsmapi.h:65
EndSampleScan_function EndSampleScan
Definition: tsmapi.h:75
SampleScanGetSampleSize_function SampleScanGetSampleSize
Definition: tsmapi.h:68
BeginSampleScan_function BeginSampleScan
Definition: tsmapi.h:72
NextSampleBlock_function NextSampleBlock
Definition: tsmapi.h:73
InitSampleScan_function InitSampleScan
Definition: tsmapi.h:71
List * parameterTypes
Definition: tsmapi.h:61
bool repeatable_across_queries
Definition: tsmapi.h:64

References TsmRoutine::BeginSampleScan, bernoulli_beginsamplescan(), bernoulli_initsamplescan(), bernoulli_nextsampletuple(), bernoulli_samplescangetsamplesize(), TsmRoutine::EndSampleScan, TsmRoutine::InitSampleScan, list_make1_oid, makeNode, TsmRoutine::NextSampleBlock, TsmRoutine::NextSampleTuple, TsmRoutine::parameterTypes, PG_RETURN_POINTER, TsmRoutine::repeatable_across_queries, TsmRoutine::repeatable_across_scans, and TsmRoutine::SampleScanGetSampleSize.