PostgreSQL Source Code  git master
system.c File Reference
#include "postgres.h"
#include <math.h>
#include "access/hash.h"
#include "access/relscan.h"
#include "access/tsmapi.h"
#include "catalog/pg_type.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "utils/builtins.h"
Include dependency graph for system.c:

Go to the source code of this file.

Data Structures

struct  SystemSamplerData
 

Functions

static void system_samplescangetsamplesize (PlannerInfo *root, RelOptInfo *baserel, List *paramexprs, BlockNumber *pages, double *tuples)
 
static void system_initsamplescan (SampleScanState *node, int eflags)
 
static void system_beginsamplescan (SampleScanState *node, Datum *params, int nparams, uint32 seed)
 
static BlockNumber system_nextsampleblock (SampleScanState *node)
 
static OffsetNumber system_nextsampletuple (SampleScanState *node, BlockNumber blockno, OffsetNumber maxoffset)
 
Datum tsm_system_handler (PG_FUNCTION_ARGS)
 

Function Documentation

◆ system_beginsamplescan()

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

Definition at line 144 of file system.c.

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

Referenced by tsm_system_handler().

148 {
149  SystemSamplerData *sampler = (SystemSamplerData *) node->tsm_state;
150  double percent = DatumGetFloat4(params[0]);
151  double dcutoff;
152 
153  if (percent < 0 || percent > 100 || isnan(percent))
154  ereport(ERROR,
155  (errcode(ERRCODE_INVALID_TABLESAMPLE_ARGUMENT),
156  errmsg("sample percentage must be between 0 and 100")));
157 
158  /*
159  * The cutoff is sample probability times (PG_UINT32_MAX + 1); we have to
160  * store that as a uint64, of course. Note that this gives strictly
161  * correct behavior at the limits of zero or one probability.
162  */
163  dcutoff = rint(((double) PG_UINT32_MAX + 1) * percent / 100);
164  sampler->cutoff = (uint64) dcutoff;
165  sampler->seed = seed;
166  sampler->nextblock = 0;
167  sampler->lt = InvalidOffsetNumber;
168 
169  /*
170  * Bulkread buffer access strategy probably makes sense unless we're
171  * scanning a very small fraction of the table. The 1% cutoff here is a
172  * guess. We should use pagemode visibility checking, since we scan all
173  * tuples on each selected page.
174  */
175  node->use_bulkread = (percent >= 1);
176  node->use_pagemode = true;
177 }
void * tsm_state
Definition: execnodes.h:1130
int errcode(int sqlerrcode)
Definition: elog.c:575
#define PG_UINT32_MAX
Definition: c.h:380
#define ERROR
Definition: elog.h:43
double rint(double x)
Definition: rint.c:22
#define ereport(elevel, rest)
Definition: elog.h:122
OffsetNumber lt
Definition: system.c:47
uint64 cutoff
Definition: system.c:44
#define InvalidOffsetNumber
Definition: off.h:26
uint32 seed
Definition: system.c:45
#define DatumGetFloat4(X)
Definition: postgres.h:686
BlockNumber nextblock
Definition: system.c:46
int errmsg(const char *fmt,...)
Definition: elog.c:797

◆ system_initsamplescan()

static void system_initsamplescan ( SampleScanState node,
int  eflags 
)
static

Definition at line 135 of file system.c.

References palloc0(), and SampleScanState::tsm_state.

Referenced by tsm_system_handler().

136 {
137  node->tsm_state = palloc0(sizeof(SystemSamplerData));
138 }
void * tsm_state
Definition: execnodes.h:1130
void * palloc0(Size size)
Definition: mcxt.c:877

◆ system_nextsampleblock()

static BlockNumber system_nextsampleblock ( SampleScanState node)
static

Definition at line 183 of file system.c.

References DatumGetUInt32, hash(), hash_any(), InvalidBlockNumber, SystemSamplerData::nextblock, SystemSamplerData::seed, SampleScanState::ss, ScanState::ss_currentScanDesc, and SampleScanState::tsm_state.

Referenced by tsm_system_handler().

184 {
185  SystemSamplerData *sampler = (SystemSamplerData *) node->tsm_state;
186  HeapScanDesc scan = node->ss.ss_currentScanDesc;
187  BlockNumber nextblock = sampler->nextblock;
188  uint32 hashinput[2];
189 
190  /*
191  * We compute the hash by applying hash_any to an array of 2 uint32's
192  * containing the block number and seed. This is efficient to set up, and
193  * with the current implementation of hash_any, it gives
194  * machine-independent results, which is a nice property for regression
195  * testing.
196  *
197  * These words in the hash input are the same throughout the block:
198  */
199  hashinput[1] = sampler->seed;
200 
201  /*
202  * Loop over block numbers until finding suitable block or reaching end of
203  * relation.
204  */
205  for (; nextblock < scan->rs_nblocks; nextblock++)
206  {
207  uint32 hash;
208 
209  hashinput[0] = nextblock;
210 
211  hash = DatumGetUInt32(hash_any((const unsigned char *) hashinput,
212  (int) sizeof(hashinput)));
213  if (hash < sampler->cutoff)
214  break;
215  }
216 
217  if (nextblock < scan->rs_nblocks)
218  {
219  /* Found a suitable block; remember where we should start next time */
220  sampler->nextblock = nextblock + 1;
221  return nextblock;
222  }
223 
224  /* Done, but let's reset nextblock to 0 for safety. */
225  sampler->nextblock = 0;
226  return InvalidBlockNumber;
227 }
#define DatumGetUInt32(X)
Definition: postgres.h:492
void * tsm_state
Definition: execnodes.h:1130
uint32 BlockNumber
Definition: block.h:31
unsigned int uint32
Definition: c.h:296
uint32 seed
Definition: system.c:45
Datum hash_any(register const unsigned char *k, register int keylen)
Definition: hashfunc.c:428
#define InvalidBlockNumber
Definition: block.h:33
BlockNumber nextblock
Definition: system.c:46
HeapScanDesc ss_currentScanDesc
Definition: execnodes.h:1105
static unsigned hash(unsigned *uv, int n)
Definition: rege_dfa.c:541
ScanState ss
Definition: execnodes.h:1125

◆ system_nextsampletuple()

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

Definition at line 242 of file system.c.

References FirstOffsetNumber, InvalidOffsetNumber, SystemSamplerData::lt, and SampleScanState::tsm_state.

Referenced by tsm_system_handler().

245 {
246  SystemSamplerData *sampler = (SystemSamplerData *) node->tsm_state;
247  OffsetNumber tupoffset = sampler->lt;
248 
249  /* Advance to next possible offset on page */
250  if (tupoffset == InvalidOffsetNumber)
251  tupoffset = FirstOffsetNumber;
252  else
253  tupoffset++;
254 
255  /* Done? */
256  if (tupoffset > maxoffset)
257  tupoffset = InvalidOffsetNumber;
258 
259  sampler->lt = tupoffset;
260 
261  return tupoffset;
262 }
void * tsm_state
Definition: execnodes.h:1130
uint16 OffsetNumber
Definition: off.h:24
#define FirstOffsetNumber
Definition: off.h:27
OffsetNumber lt
Definition: system.c:47
#define InvalidOffsetNumber
Definition: off.h:26

◆ system_samplescangetsamplesize()

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

Definition at line 93 of file system.c.

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

Referenced by tsm_system_handler().

98 {
99  Node *pctnode;
100  float4 samplefract;
101 
102  /* Try to extract an estimate for the sample percentage */
103  pctnode = (Node *) linitial(paramexprs);
104  pctnode = estimate_expression_value(root, pctnode);
105 
106  if (IsA(pctnode, Const) &&
107  !((Const *) pctnode)->constisnull)
108  {
109  samplefract = DatumGetFloat4(((Const *) pctnode)->constvalue);
110  if (samplefract >= 0 && samplefract <= 100 && !isnan(samplefract))
111  samplefract /= 100.0f;
112  else
113  {
114  /* Default samplefract if the value is bogus */
115  samplefract = 0.1f;
116  }
117  }
118  else
119  {
120  /* Default samplefract if we didn't obtain a non-null Const */
121  samplefract = 0.1f;
122  }
123 
124  /* We'll visit a sample of the pages ... */
125  *pages = clamp_row_est(baserel->pages * samplefract);
126 
127  /* ... and hopefully get a representative number of tuples from them */
128  *tuples = clamp_row_est(baserel->tuples * samplefract);
129 }
#define IsA(nodeptr, _type_)
Definition: nodes.h:562
Node * estimate_expression_value(PlannerInfo *root, Node *node)
Definition: clauses.c:2492
double tuples
Definition: relation.h:625
Definition: nodes.h:511
#define linitial(l)
Definition: pg_list.h:111
float float4
Definition: c.h:428
BlockNumber pages
Definition: relation.h:624
#define DatumGetFloat4(X)
Definition: postgres.h:686
double clamp_row_est(double nrows)
Definition: costsize.c:174

◆ tsm_system_handler()

Datum tsm_system_handler ( PG_FUNCTION_ARGS  )

Definition at line 72 of file system.c.

References TsmRoutine::BeginSampleScan, TsmRoutine::EndSampleScan, FLOAT4OID, TsmRoutine::InitSampleScan, list_make1_oid, makeNode, TsmRoutine::NextSampleBlock, TsmRoutine::NextSampleTuple, TsmRoutine::parameterTypes, PG_RETURN_POINTER, TsmRoutine::repeatable_across_queries, TsmRoutine::repeatable_across_scans, TsmRoutine::SampleScanGetSampleSize, system_beginsamplescan(), system_initsamplescan(), system_nextsampleblock(), system_nextsampletuple(), and system_samplescangetsamplesize().

73 {
75 
77  tsm->repeatable_across_queries = true;
78  tsm->repeatable_across_scans = true;
84  tsm->EndSampleScan = NULL;
85 
86  PG_RETURN_POINTER(tsm);
87 }
InitSampleScan_function InitSampleScan
Definition: tsmapi.h:70
#define PG_RETURN_POINTER(x)
Definition: fmgr.h:321
static OffsetNumber system_nextsampletuple(SampleScanState *node, BlockNumber blockno, OffsetNumber maxoffset)
Definition: system.c:242
bool repeatable_across_queries
Definition: tsmapi.h:63
static BlockNumber system_nextsampleblock(SampleScanState *node)
Definition: system.c:183
static void system_initsamplescan(SampleScanState *node, int eflags)
Definition: system.c:135
NextSampleTuple_function NextSampleTuple
Definition: tsmapi.h:73
NextSampleBlock_function NextSampleBlock
Definition: tsmapi.h:72
SampleScanGetSampleSize_function SampleScanGetSampleSize
Definition: tsmapi.h:67
#define FLOAT4OID
Definition: pg_type.h:416
#define list_make1_oid(x1)
Definition: pg_list.h:151
#define makeNode(_type_)
Definition: nodes.h:559
BeginSampleScan_function BeginSampleScan
Definition: tsmapi.h:71
bool repeatable_across_scans
Definition: tsmapi.h:64
static void system_beginsamplescan(SampleScanState *node, Datum *params, int nparams, uint32 seed)
Definition: system.c:144
List * parameterTypes
Definition: tsmapi.h:60
static void system_samplescangetsamplesize(PlannerInfo *root, RelOptInfo *baserel, List *paramexprs, BlockNumber *pages, double *tuples)
Definition: system.c:93
EndSampleScan_function EndSampleScan
Definition: tsmapi.h:74