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Commit73c954d

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tableam: sample scan.
This moves sample scan support to below tableam. It's not optional asthere is, in contrast to e.g. bitmap heap scans, no alternative way toperform tablesample queries. If an AM can't deal with the block basedAPI, it will have to throw an ERROR.The tableam callbacks for this are block based, but given the currentTsmRoutine interface, that seems to be required.The new interface doesn't require TsmRoutines to perform visibilitychecks anymore - that requires the TsmRoutine to know details aboutthe AM, which we want to avoid. To continue to allow taking thereturned number of tuples account SampleScanState now has a donetuplesfield (which previously e.g. existed in SystemRowsSamplerData), whichis only incremented after the visibility check succeeds.Author: Andres FreundDiscussion:https://postgr.es/m/20180703070645.wchpu5muyto5n647@alap3.anarazel.de
1 parent4bb5023 commit73c954d

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10 files changed

+382
-312
lines changed

10 files changed

+382
-312
lines changed

‎contrib/tsm_system_rows/tsm_system_rows.c

Lines changed: 15 additions & 71 deletions
Original file line numberDiff line numberDiff line change
@@ -28,7 +28,6 @@
2828

2929
#include"postgres.h"
3030

31-
#include"access/heapam.h"
3231
#include"access/relscan.h"
3332
#include"access/tsmapi.h"
3433
#include"catalog/pg_type.h"
@@ -46,7 +45,6 @@ typedef struct
4645
{
4746
uint32seed;/* random seed */
4847
int64ntuples;/* number of tuples to return */
49-
int64donetuples;/* number of tuples already returned */
5048
OffsetNumberlt;/* last tuple returned from current block */
5149
BlockNumberdoneblocks;/* number of already-scanned blocks */
5250
BlockNumberlb;/* last block visited */
@@ -67,11 +65,10 @@ static void system_rows_beginsamplescan(SampleScanState *node,
6765
Datum*params,
6866
intnparams,
6967
uint32seed);
70-
staticBlockNumbersystem_rows_nextsampleblock(SampleScanState*node);
68+
staticBlockNumbersystem_rows_nextsampleblock(SampleScanState*node,BlockNumbernblocks);
7169
staticOffsetNumbersystem_rows_nextsampletuple(SampleScanState*node,
7270
BlockNumberblockno,
7371
OffsetNumbermaxoffset);
74-
staticboolSampleOffsetVisible(OffsetNumbertupoffset,HeapScanDescscan);
7572
staticuint32random_relative_prime(uint32n,SamplerRandomStaterandstate);
7673

7774

@@ -187,7 +184,6 @@ system_rows_beginsamplescan(SampleScanState *node,
187184

188185
sampler->seed=seed;
189186
sampler->ntuples=ntuples;
190-
sampler->donetuples=0;
191187
sampler->lt=InvalidOffsetNumber;
192188
sampler->doneblocks=0;
193189
/* lb will be initialized during first NextSampleBlock call */
@@ -206,11 +202,9 @@ system_rows_beginsamplescan(SampleScanState *node,
206202
* Uses linear probing algorithm for picking next block.
207203
*/
208204
staticBlockNumber
209-
system_rows_nextsampleblock(SampleScanState*node)
205+
system_rows_nextsampleblock(SampleScanState*node,BlockNumbernblocks)
210206
{
211207
SystemRowsSamplerData*sampler= (SystemRowsSamplerData*)node->tsm_state;
212-
TableScanDescscan=node->ss.ss_currentScanDesc;
213-
HeapScanDeschscan= (HeapScanDesc)scan;
214208

215209
/* First call within scan? */
216210
if (sampler->doneblocks==0)
@@ -222,14 +216,14 @@ system_rows_nextsampleblock(SampleScanState *node)
222216
SamplerRandomStaterandstate;
223217

224218
/* If relation is empty, there's nothing to scan */
225-
if (hscan->rs_nblocks==0)
219+
if (nblocks==0)
226220
returnInvalidBlockNumber;
227221

228222
/* We only need an RNG during this setup step */
229223
sampler_random_init_state(sampler->seed,randstate);
230224

231225
/* Compute nblocks/firstblock/step only once per query */
232-
sampler->nblocks=hscan->rs_nblocks;
226+
sampler->nblocks=nblocks;
233227

234228
/* Choose random starting block within the relation */
235229
/* (Actually this is the predecessor of the first block visited) */
@@ -246,7 +240,7 @@ system_rows_nextsampleblock(SampleScanState *node)
246240

247241
/* If we've read all blocks or returned all needed tuples, we're done */
248242
if (++sampler->doneblocks>sampler->nblocks||
249-
sampler->donetuples >=sampler->ntuples)
243+
node->donetuples >=sampler->ntuples)
250244
returnInvalidBlockNumber;
251245

252246
/*
@@ -259,7 +253,7 @@ system_rows_nextsampleblock(SampleScanState *node)
259253
{
260254
/* Advance lb, using uint64 arithmetic to forestall overflow */
261255
sampler->lb= ((uint64)sampler->lb+sampler->step) %sampler->nblocks;
262-
}while (sampler->lb >=hscan->rs_nblocks);
256+
}while (sampler->lb >=nblocks);
263257

264258
returnsampler->lb;
265259
}
@@ -279,77 +273,27 @@ system_rows_nextsampletuple(SampleScanState *node,
279273
OffsetNumbermaxoffset)
280274
{
281275
SystemRowsSamplerData*sampler= (SystemRowsSamplerData*)node->tsm_state;
282-
TableScanDescscan=node->ss.ss_currentScanDesc;
283-
HeapScanDeschscan= (HeapScanDesc)scan;
284276
OffsetNumbertupoffset=sampler->lt;
285277

286278
/* Quit if we've returned all needed tuples */
287-
if (sampler->donetuples >=sampler->ntuples)
279+
if (node->donetuples >=sampler->ntuples)
288280
returnInvalidOffsetNumber;
289281

290-
/*
291-
* Because we should only count visible tuples as being returned, we need
292-
* to search for a visible tuple rather than just let the core code do it.
293-
*/
294-
295-
/* We rely on the data accumulated in pagemode access */
296-
Assert(scan->rs_pageatatime);
297-
for (;;)
298-
{
299-
/* Advance to next possible offset on page */
300-
if (tupoffset==InvalidOffsetNumber)
301-
tupoffset=FirstOffsetNumber;
302-
else
303-
tupoffset++;
304-
305-
/* Done? */
306-
if (tupoffset>maxoffset)
307-
{
308-
tupoffset=InvalidOffsetNumber;
309-
break;
310-
}
282+
/* Advance to next possible offset on page */
283+
if (tupoffset==InvalidOffsetNumber)
284+
tupoffset=FirstOffsetNumber;
285+
else
286+
tupoffset++;
311287

312-
/* Found a candidate? */
313-
if (SampleOffsetVisible(tupoffset,hscan))
314-
{
315-
sampler->donetuples++;
316-
break;
317-
}
318-
}
288+
/* Done? */
289+
if (tupoffset>maxoffset)
290+
tupoffset=InvalidOffsetNumber;
319291

320292
sampler->lt=tupoffset;
321293

322294
returntupoffset;
323295
}
324296

325-
/*
326-
* Check if tuple offset is visible
327-
*
328-
* In pageatatime mode, heapgetpage() already did visibility checks,
329-
* so just look at the info it left in rs_vistuples[].
330-
*/
331-
staticbool
332-
SampleOffsetVisible(OffsetNumbertupoffset,HeapScanDescscan)
333-
{
334-
intstart=0,
335-
end=scan->rs_ntuples-1;
336-
337-
while (start <=end)
338-
{
339-
intmid= (start+end) /2;
340-
OffsetNumbercuroffset=scan->rs_vistuples[mid];
341-
342-
if (tupoffset==curoffset)
343-
return true;
344-
elseif (tupoffset<curoffset)
345-
end=mid-1;
346-
else
347-
start=mid+1;
348-
}
349-
350-
return false;
351-
}
352-
353297
/*
354298
* Compute greatest common divisor of two uint32's.
355299
*/

‎contrib/tsm_system_time/tsm_system_time.c

Lines changed: 5 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -26,7 +26,6 @@
2626

2727
#include<math.h>
2828

29-
#include"access/heapam.h"
3029
#include"access/relscan.h"
3130
#include"access/tsmapi.h"
3231
#include"catalog/pg_type.h"
@@ -66,7 +65,7 @@ static void system_time_beginsamplescan(SampleScanState *node,
6665
Datum*params,
6766
intnparams,
6867
uint32seed);
69-
staticBlockNumbersystem_time_nextsampleblock(SampleScanState*node);
68+
staticBlockNumbersystem_time_nextsampleblock(SampleScanState*node,BlockNumbernblocks);
7069
staticOffsetNumbersystem_time_nextsampletuple(SampleScanState*node,
7170
BlockNumberblockno,
7271
OffsetNumbermaxoffset);
@@ -213,11 +212,9 @@ system_time_beginsamplescan(SampleScanState *node,
213212
* Uses linear probing algorithm for picking next block.
214213
*/
215214
staticBlockNumber
216-
system_time_nextsampleblock(SampleScanState*node)
215+
system_time_nextsampleblock(SampleScanState*node,BlockNumbernblocks)
217216
{
218217
SystemTimeSamplerData*sampler= (SystemTimeSamplerData*)node->tsm_state;
219-
TableScanDescscan=node->ss.ss_currentScanDesc;
220-
HeapScanDeschscan= (HeapScanDesc)scan;
221218
instr_timecur_time;
222219

223220
/* First call within scan? */
@@ -230,14 +227,14 @@ system_time_nextsampleblock(SampleScanState *node)
230227
SamplerRandomStaterandstate;
231228

232229
/* If relation is empty, there's nothing to scan */
233-
if (hscan->rs_nblocks==0)
230+
if (nblocks==0)
234231
returnInvalidBlockNumber;
235232

236233
/* We only need an RNG during this setup step */
237234
sampler_random_init_state(sampler->seed,randstate);
238235

239236
/* Compute nblocks/firstblock/step only once per query */
240-
sampler->nblocks=hscan->rs_nblocks;
237+
sampler->nblocks=nblocks;
241238

242239
/* Choose random starting block within the relation */
243240
/* (Actually this is the predecessor of the first block visited) */
@@ -273,7 +270,7 @@ system_time_nextsampleblock(SampleScanState *node)
273270
{
274271
/* Advance lb, using uint64 arithmetic to forestall overflow */
275272
sampler->lb= ((uint64)sampler->lb+sampler->step) %sampler->nblocks;
276-
}while (sampler->lb >=hscan->rs_nblocks);
273+
}while (sampler->lb >=nblocks);
277274

278275
returnsampler->lb;
279276
}

‎doc/src/sgml/tablesample-method.sgml

Lines changed: 4 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -227,7 +227,7 @@ BeginSampleScan (SampleScanState *node,
227227
<para>
228228
<programlisting>
229229
BlockNumber
230-
NextSampleBlock (SampleScanState *node);
230+
NextSampleBlock (SampleScanState *node, BlockNumber nblocks);
231231
</programlisting>
232232

233233
Returns the block number of the next page to be scanned, or
@@ -262,10 +262,9 @@ NextSampleTuple (SampleScanState *node,
262262
numbers in the range <literal>1 .. maxoffset</literal> actually contain valid
263263
tuples. This is not normally a problem since the core code ignores
264264
requests to sample missing or invisible tuples; that should not result in
265-
any bias in the sample. However, if necessary, the function can
266-
examine <literal>node-&gt;ss.ss_currentScanDesc-&gt;rs_vistuples[]</literal>
267-
to identify which tuples are valid and visible. (This
268-
requires <literal>node-&gt;use_pagemode</literal> to be <literal>true</literal>.)
265+
any bias in the sample. However, if necessary, the function can use
266+
<literal>node-&gt;donetuples</literal> to examine how many of the tuples
267+
it returned were vlaid and visible.
269268
</para>
270269
</note>
271270

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