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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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22
src/backend/optimizer/util/pathnode.c
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@ -705,6 +705,26 @@ create_seqscan_path(PlannerInfo *root, RelOptInfo *rel, Relids required_outer)
return pathnode;
}
/*
* create_samplescan_path
* Like seqscan but uses sampling function while scanning.
*/
Path *
create_samplescan_path(PlannerInfo *root, RelOptInfo *rel, Relids required_outer)
{
Path *pathnode = makeNode(Path);
pathnode->pathtype = T_SampleScan;
pathnode->parent = rel;
pathnode->param_info = get_baserel_parampathinfo(root, rel,
required_outer);
pathnode->pathkeys = NIL; /* samplescan has unordered result */
cost_samplescan(pathnode, root, rel);
return pathnode;
}
/*
* create_index_path
* Creates a path node for an index scan.
@ -1778,6 +1798,8 @@ reparameterize_path(PlannerInfo *root, Path *path,
case T_SubqueryScan:
return create_subqueryscan_path(root, rel, path->pathkeys,
required_outer);
case T_SampleScan:
return (Path *) create_samplescan_path(root, rel, required_outer);
default:
break;
}