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TABLESAMPLE, SQL Standard and extensible
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
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@ -71,6 +71,10 @@ static void set_plain_rel_size(PlannerInfo *root, RelOptInfo *rel,
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RangeTblEntry *rte);
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static void set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
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RangeTblEntry *rte);
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static void set_tablesample_rel_size(PlannerInfo *root, RelOptInfo *rel,
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RangeTblEntry *rte);
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static void set_tablesample_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
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RangeTblEntry *rte);
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static void set_foreign_size(PlannerInfo *root, RelOptInfo *rel,
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RangeTblEntry *rte);
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static void set_foreign_pathlist(PlannerInfo *root, RelOptInfo *rel,
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@ -265,6 +269,11 @@ set_rel_size(PlannerInfo *root, RelOptInfo *rel,
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/* Foreign table */
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set_foreign_size(root, rel, rte);
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}
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else if (rte->tablesample != NULL)
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{
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/* Sampled relation */
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set_tablesample_rel_size(root, rel, rte);
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}
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else
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{
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/* Plain relation */
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@ -332,6 +341,11 @@ set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
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/* Foreign table */
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set_foreign_pathlist(root, rel, rte);
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}
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else if (rte->tablesample != NULL)
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{
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/* Build sample scan on relation */
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set_tablesample_rel_pathlist(root, rel, rte);
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}
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else
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{
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/* Plain relation */
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@ -417,6 +431,41 @@ set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
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create_tidscan_paths(root, rel);
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}
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/*
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* set_tablesample_rel_size
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* Set size estimates for a sampled relation.
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*/
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static void
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set_tablesample_rel_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
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{
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/* Mark rel with estimated output rows, width, etc */
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set_baserel_size_estimates(root, rel);
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}
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/*
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* set_tablesample_rel_pathlist
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* Build access paths for a sampled relation
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*
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* There is only one possible path - sampling scan
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*/
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static void
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set_tablesample_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
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{
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Relids required_outer;
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Path *path;
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/*
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* We don't support pushing join clauses into the quals of a seqscan, but
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* it could still have required parameterization due to LATERAL refs in
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* its tlist.
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*/
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required_outer = rel->lateral_relids;
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/* We only do sample scan if it was requested */
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path = create_samplescan_path(root, rel, required_outer);
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rel->pathlist = list_make1(path);
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}
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/*
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* set_foreign_size
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* Set size estimates for a foreign table RTE
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