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TABLESAMPLE, SQL Standard and extensible

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Add a TABLESAMPLE clause to SELECT statements that allows
user to specify random BERNOULLI sampling or block level
SYSTEM sampling. Implementation allows for extensible
sampling functions to be written, using a standard API.
Basic version follows SQLStandard exactly. Usable
concrete use cases for the sampling API follow in later
commits.

Petr Jelinek

Reviewed by Michael Paquier and Simon Riggs
This commit is contained in:
Simon Riggs
2015-05-15 14:37:10 -04:00
parent 11a83bbedd
commit f6d208d6e5
66 changed files with 2756 additions and 40 deletions
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21
src/backend/commands/explain.c
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@ -731,6 +731,7 @@ ExplainPreScanNode(PlanState *planstate, Bitmapset **rels_used)
case T_ValuesScan:
case T_CteScan:
case T_WorkTableScan:
case T_SampleScan:
*rels_used = bms_add_member(*rels_used,
((Scan *) plan)->scanrelid);
break;
@ -967,6 +968,21 @@ ExplainNode(PlanState *planstate, List *ancestors,
else
pname = sname;
break;
case T_SampleScan:
{
/*
* Fetch the tablesample method name from RTE.
*
* It would be nice to also show parameters, but since we
* support arbitrary expressions as parameter it might get
* quite messy.
*/
RangeTblEntry *rte;
rte = rt_fetch(((SampleScan *) plan)->scanrelid, es->rtable);
custom_name = get_tablesample_method_name(rte->tablesample->tsmid);
pname = psprintf("Sample Scan (%s)", custom_name);
}
break;
case T_Material:
pname = sname = "Materialize";
break;
@ -1089,6 +1105,9 @@ ExplainNode(PlanState *planstate, List *ancestors,
if (((Scan *) plan)->scanrelid > 0)
ExplainScanTarget((Scan *) plan, es);
break;
case T_SampleScan:
ExplainScanTarget((Scan *) plan, es);
break;
case T_IndexScan:
{
IndexScan *indexscan = (IndexScan *) plan;
@ -1339,6 +1358,7 @@ ExplainNode(PlanState *planstate, List *ancestors,
case T_CteScan:
case T_WorkTableScan:
case T_SubqueryScan:
case T_SampleScan:
show_scan_qual(plan->qual, "Filter", planstate, ancestors, es);
if (plan->qual)
show_instrumentation_count("Rows Removed by Filter", 1,
@ -2238,6 +2258,7 @@ ExplainTargetRel(Plan *plan, Index rti, ExplainState *es)
case T_TidScan:
case T_ForeignScan:
case T_CustomScan:
case T_SampleScan:
case T_ModifyTable:
/* Assert it's on a real relation */
Assert(rte->rtekind == RTE_RELATION);