PostgreSQL Source Code  git master
tsm_system_time.c File Reference
#include "postgres.h"
#include <math.h>
#include "access/tsmapi.h"
#include "catalog/pg_type.h"
#include "miscadmin.h"
#include "optimizer/optimizer.h"
#include "utils/sampling.h"
#include "utils/spccache.h"
Include dependency graph for tsm_system_time.c:

Go to the source code of this file.

Data Structures

struct  SystemTimeSamplerData
 

Functions

 PG_FUNCTION_INFO_V1 (tsm_system_time_handler)
 
static void system_time_samplescangetsamplesize (PlannerInfo *root, RelOptInfo *baserel, List *paramexprs, BlockNumber *pages, double *tuples)
 
static void system_time_initsamplescan (SampleScanState *node, int eflags)
 
static void system_time_beginsamplescan (SampleScanState *node, Datum *params, int nparams, uint32 seed)
 
static BlockNumber system_time_nextsampleblock (SampleScanState *node, BlockNumber nblocks)
 
static OffsetNumber system_time_nextsampletuple (SampleScanState *node, BlockNumber blockno, OffsetNumber maxoffset)
 
static uint32 random_relative_prime (uint32 n, pg_prng_state *randstate)
 
Datum tsm_system_time_handler (PG_FUNCTION_ARGS)
 
static uint32 gcd (uint32 a, uint32 b)
 

Variables

 PG_MODULE_MAGIC
 

Function Documentation

◆ gcd()

static uint32 gcd ( uint32  a,
uint32  b 
)
static

Definition at line 313 of file tsm_system_time.c.

314 {
315  uint32 c;
316 
317  while (a != 0)
318  {
319  c = a;
320  a = b % a;
321  b = c;
322  }
323 
324  return b;
325 }
unsigned int uint32
Definition: c.h:506
int b
Definition: isn.c:69
int a
Definition: isn.c:68
char * c

References a, and b.

Referenced by random_relative_prime().

◆ PG_FUNCTION_INFO_V1()

PG_FUNCTION_INFO_V1 ( tsm_system_time_handler  )

◆ random_relative_prime()

static uint32 random_relative_prime ( uint32  n,
pg_prng_state randstate 
)
static

Definition at line 332 of file tsm_system_time.c.

333 {
334  uint32 r;
335 
336  /* Safety check to avoid infinite loop or zero result for small n. */
337  if (n <= 1)
338  return 1;
339 
340  /*
341  * This should only take 2 or 3 iterations as the probability of 2 numbers
342  * being relatively prime is ~61%; but just in case, we'll include a
343  * CHECK_FOR_INTERRUPTS in the loop.
344  */
345  do
346  {
348  r = (uint32) (sampler_random_fract(randstate) * n);
349  } while (r == 0 || gcd(r, n) > 1);
350 
351  return r;
352 }
#define CHECK_FOR_INTERRUPTS()
Definition: miscadmin.h:122
double sampler_random_fract(pg_prng_state *randstate)
Definition: sampling.c:241
static uint32 gcd(uint32 a, uint32 b)

References CHECK_FOR_INTERRUPTS, gcd(), and sampler_random_fract().

Referenced by system_time_nextsampleblock().

◆ system_time_beginsamplescan()

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

Definition at line 187 of file tsm_system_time.c.

191 {
193  double millis = DatumGetFloat8(params[0]);
194 
195  if (millis < 0 || isnan(millis))
196  ereport(ERROR,
197  (errcode(ERRCODE_INVALID_TABLESAMPLE_ARGUMENT),
198  errmsg("sample collection time must not be negative")));
199 
200  sampler->seed = seed;
201  sampler->millis = millis;
202  sampler->lt = InvalidOffsetNumber;
203  sampler->doneblocks = 0;
204  /* start_time, lb will be initialized during first NextSampleBlock call */
205  /* we intentionally do not change nblocks/firstblock/step here */
206 }
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 float8 DatumGetFloat8(Datum X)
Definition: postgres.h:494
void * tsm_state
Definition: execnodes.h:1601

References DatumGetFloat8(), SystemTimeSamplerData::doneblocks, ereport, errcode(), errmsg(), ERROR, InvalidOffsetNumber, SystemTimeSamplerData::lt, SystemTimeSamplerData::millis, SystemTimeSamplerData::seed, and SampleScanState::tsm_state.

Referenced by tsm_system_time_handler().

◆ system_time_initsamplescan()

static void system_time_initsamplescan ( SampleScanState node,
int  eflags 
)
static

Definition at line 177 of file tsm_system_time.c.

178 {
179  node->tsm_state = palloc0(sizeof(SystemTimeSamplerData));
180  /* Note the above leaves tsm_state->step equal to zero */
181 }
void * palloc0(Size size)
Definition: mcxt.c:1347

References palloc0(), and SampleScanState::tsm_state.

Referenced by tsm_system_time_handler().

◆ system_time_nextsampleblock()

static BlockNumber system_time_nextsampleblock ( SampleScanState node,
BlockNumber  nblocks 
)
static

Definition at line 214 of file tsm_system_time.c.

215 {
217  instr_time cur_time;
218 
219  /* First call within scan? */
220  if (sampler->doneblocks == 0)
221  {
222  /* First scan within query? */
223  if (sampler->step == 0)
224  {
225  /* Initialize now that we have scan descriptor */
226  pg_prng_state randstate;
227 
228  /* If relation is empty, there's nothing to scan */
229  if (nblocks == 0)
230  return InvalidBlockNumber;
231 
232  /* We only need an RNG during this setup step */
233  sampler_random_init_state(sampler->seed, &randstate);
234 
235  /* Compute nblocks/firstblock/step only once per query */
236  sampler->nblocks = nblocks;
237 
238  /* Choose random starting block within the relation */
239  /* (Actually this is the predecessor of the first block visited) */
240  sampler->firstblock = sampler_random_fract(&randstate) *
241  sampler->nblocks;
242 
243  /* Find relative prime as step size for linear probing */
244  sampler->step = random_relative_prime(sampler->nblocks, &randstate);
245  }
246 
247  /* Reinitialize lb and start_time */
248  sampler->lb = sampler->firstblock;
250  }
251 
252  /* If we've read all blocks in relation, we're done */
253  if (++sampler->doneblocks > sampler->nblocks)
254  return InvalidBlockNumber;
255 
256  /* If we've used up all the allotted time, we're done */
257  INSTR_TIME_SET_CURRENT(cur_time);
258  INSTR_TIME_SUBTRACT(cur_time, sampler->start_time);
259  if (INSTR_TIME_GET_MILLISEC(cur_time) >= sampler->millis)
260  return InvalidBlockNumber;
261 
262  /*
263  * It's probably impossible for scan->rs_nblocks to decrease between scans
264  * within a query; but just in case, loop until we select a block number
265  * less than scan->rs_nblocks. We don't care if scan->rs_nblocks has
266  * increased since the first scan.
267  */
268  do
269  {
270  /* Advance lb, using uint64 arithmetic to forestall overflow */
271  sampler->lb = ((uint64) sampler->lb + sampler->step) % sampler->nblocks;
272  } while (sampler->lb >= nblocks);
273 
274  return sampler->lb;
275 }
#define InvalidBlockNumber
Definition: block.h:33
#define INSTR_TIME_SET_CURRENT(t)
Definition: instr_time.h:122
#define INSTR_TIME_SUBTRACT(x, y)
Definition: instr_time.h:181
#define INSTR_TIME_GET_MILLISEC(t)
Definition: instr_time.h:191
if(TABLE==NULL||TABLE_index==NULL)
Definition: isn.c:76
void sampler_random_init_state(uint32 seed, pg_prng_state *randstate)
Definition: sampling.c:234
static uint32 random_relative_prime(uint32 n, pg_prng_state *randstate)

References SystemTimeSamplerData::doneblocks, SystemTimeSamplerData::firstblock, if(), INSTR_TIME_GET_MILLISEC, INSTR_TIME_SET_CURRENT, INSTR_TIME_SUBTRACT, InvalidBlockNumber, SystemTimeSamplerData::lb, SystemTimeSamplerData::millis, SystemTimeSamplerData::nblocks, random_relative_prime(), sampler_random_fract(), sampler_random_init_state(), SystemTimeSamplerData::seed, SystemTimeSamplerData::start_time, SystemTimeSamplerData::step, and SampleScanState::tsm_state.

Referenced by tsm_system_time_handler().

◆ system_time_nextsampletuple()

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

Definition at line 287 of file tsm_system_time.c.

290 {
292  OffsetNumber tupoffset = sampler->lt;
293 
294  /* Advance to next possible offset on page */
295  if (tupoffset == InvalidOffsetNumber)
296  tupoffset = FirstOffsetNumber;
297  else
298  tupoffset++;
299 
300  /* Done? */
301  if (tupoffset > maxoffset)
302  tupoffset = InvalidOffsetNumber;
303 
304  sampler->lt = tupoffset;
305 
306  return tupoffset;
307 }
uint16 OffsetNumber
Definition: off.h:24
#define FirstOffsetNumber
Definition: off.h:27

References FirstOffsetNumber, if(), InvalidOffsetNumber, SystemTimeSamplerData::lt, and SampleScanState::tsm_state.

Referenced by tsm_system_time_handler().

◆ system_time_samplescangetsamplesize()

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

Definition at line 102 of file tsm_system_time.c.

107 {
108  Node *limitnode;
109  double millis;
110  double spc_random_page_cost;
111  double npages;
112  double ntuples;
113 
114  /* Try to extract an estimate for the limit time spec */
115  limitnode = (Node *) linitial(paramexprs);
116  limitnode = estimate_expression_value(root, limitnode);
117 
118  if (IsA(limitnode, Const) &&
119  !((Const *) limitnode)->constisnull)
120  {
121  millis = DatumGetFloat8(((Const *) limitnode)->constvalue);
122  if (millis < 0 || isnan(millis))
123  {
124  /* Default millis if the value is bogus */
125  millis = 1000;
126  }
127  }
128  else
129  {
130  /* Default millis if we didn't obtain a non-null Const */
131  millis = 1000;
132  }
133 
134  /* Get the planner's idea of cost per page read */
136  &spc_random_page_cost,
137  NULL);
138 
139  /*
140  * Estimate the number of pages we can read by assuming that the cost
141  * figure is expressed in milliseconds. This is completely, unmistakably
142  * bogus, but we have to do something to produce an estimate and there's
143  * no better answer.
144  */
145  if (spc_random_page_cost > 0)
146  npages = millis / spc_random_page_cost;
147  else
148  npages = millis; /* even more bogus, but whatcha gonna do? */
149 
150  /* Clamp to sane value */
151  npages = clamp_row_est(Min((double) baserel->pages, npages));
152 
153  if (baserel->tuples > 0 && baserel->pages > 0)
154  {
155  /* Estimate number of tuples returned based on tuple density */
156  double density = baserel->tuples / (double) baserel->pages;
157 
158  ntuples = npages * density;
159  }
160  else
161  {
162  /* For lack of data, assume one tuple per page */
163  ntuples = npages;
164  }
165 
166  /* Clamp to the estimated relation size */
167  ntuples = clamp_row_est(Min(baserel->tuples, ntuples));
168 
169  *pages = npages;
170  *tuples = ntuples;
171 }
#define Min(x, y)
Definition: c.h:995
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:1886
void get_tablespace_page_costs(Oid spcid, double *spc_random_page_cost, double *spc_seq_page_cost)
Definition: spccache.c:182
Definition: nodes.h:129
Cardinality tuples
Definition: pathnodes.h:949
BlockNumber pages
Definition: pathnodes.h:948
Oid reltablespace
Definition: pathnodes.h:920

References clamp_row_est(), DatumGetFloat8(), estimate_expression_value(), get_tablespace_page_costs(), IsA, linitial, Min, RelOptInfo::pages, RelOptInfo::reltablespace, root, and RelOptInfo::tuples.

Referenced by tsm_system_time_handler().

◆ tsm_system_time_handler()

Datum tsm_system_time_handler ( PG_FUNCTION_ARGS  )

Definition at line 78 of file tsm_system_time.c.

79 {
81 
82  tsm->parameterTypes = list_make1_oid(FLOAT8OID);
83 
84  /* See notes at head of file */
85  tsm->repeatable_across_queries = false;
86  tsm->repeatable_across_scans = false;
87 
93  tsm->EndSampleScan = NULL;
94 
95  PG_RETURN_POINTER(tsm);
96 }
#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
static void system_time_samplescangetsamplesize(PlannerInfo *root, RelOptInfo *baserel, List *paramexprs, BlockNumber *pages, double *tuples)
static void system_time_beginsamplescan(SampleScanState *node, Datum *params, int nparams, uint32 seed)
static void system_time_initsamplescan(SampleScanState *node, int eflags)
static OffsetNumber system_time_nextsampletuple(SampleScanState *node, BlockNumber blockno, OffsetNumber maxoffset)
static BlockNumber system_time_nextsampleblock(SampleScanState *node, BlockNumber nblocks)

References TsmRoutine::BeginSampleScan, 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, TsmRoutine::SampleScanGetSampleSize, system_time_beginsamplescan(), system_time_initsamplescan(), system_time_nextsampleblock(), system_time_nextsampletuple(), and system_time_samplescangetsamplesize().

Variable Documentation

◆ PG_MODULE_MAGIC

PG_MODULE_MAGIC

Definition at line 36 of file tsm_system_time.c.