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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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50
src/backend/utils/adt/ruleutils.c
View File

@ -32,6 +32,7 @@
#include "catalog/pg_opclass.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_tablesample_method.h"
#include "catalog/pg_trigger.h"
#include "catalog/pg_type.h"
#include "commands/defrem.h"
@ -345,6 +346,8 @@ static void make_ruledef(StringInfo buf, HeapTuple ruletup, TupleDesc rulettc,
int prettyFlags);
static void make_viewdef(StringInfo buf, HeapTuple ruletup, TupleDesc rulettc,
int prettyFlags, int wrapColumn);
static void get_tablesample_def(TableSampleClause *tablesample,
deparse_context *context);
static void get_query_def(Query *query, StringInfo buf, List *parentnamespace,
TupleDesc resultDesc,
int prettyFlags, int wrapColumn, int startIndent);
@ -4220,6 +4223,50 @@ make_viewdef(StringInfo buf, HeapTuple ruletup, TupleDesc rulettc,
heap_close(ev_relation, AccessShareLock);
}
/* ----------
* get_tablesample_def - Convert TableSampleClause back to SQL
* ----------
*/
static void
get_tablesample_def(TableSampleClause *tablesample, deparse_context *context)
{
StringInfo buf = context->buf;
HeapTuple tuple;
Form_pg_tablesample_method tsm;
char *tsmname;
int nargs;
ListCell *l;
/* Load the tablesample method */
tuple = SearchSysCache1(TABLESAMPLEMETHODOID, ObjectIdGetDatum(tablesample->tsmid));
if (!HeapTupleIsValid(tuple))
ereport(ERROR,
(errcode(ERRCODE_UNDEFINED_OBJECT),
errmsg("cache lookup failed for tablesample method %u",
tablesample->tsmid)));
tsm = (Form_pg_tablesample_method) GETSTRUCT(tuple);
tsmname = NameStr(tsm->tsmname);
appendStringInfo(buf, " TABLESAMPLE %s (", quote_identifier(tsmname));
ReleaseSysCache(tuple);
nargs = 0;
foreach(l, tablesample->args)
{
if (nargs++ > 0)
appendStringInfoString(buf, ", ");
get_rule_expr((Node *) lfirst(l), context, true);
}
appendStringInfoChar(buf, ')');
if (tablesample->repeatable != NULL)
{
appendStringInfoString(buf, " REPEATABLE (");
get_rule_expr(tablesample->repeatable, context, true);
appendStringInfoChar(buf, ')');
}
}
/* ----------
* get_query_def - Parse back one query parsetree
@ -8529,6 +8576,9 @@ get_from_clause_item(Node *jtnode, Query *query, deparse_context *context)
only_marker(rte),
generate_relation_name(rte->relid,
context->namespaces));
if (rte->tablesample)
get_tablesample_def(rte->tablesample, context);
break;
case RTE_SUBQUERY:
/* Subquery RTE */