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Sample postgres_fdw tables remotely during ANALYZE

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When collecting ANALYZE sample on foreign tables, postgres_fdw fetched
all rows and performed the sampling locally. For large tables this means
transferring and immediately discarding large amounts of data.

This commit allows the sampling to be performed on the remote server,
transferring only the much smaller sample. The sampling is performed
using the built-in TABLESAMPLE methods (system, bernoulli) or random()
function, depending on the remote server version.

Remote sampling can be enabled by analyze_sampling on the foreign server
and/or foreign table, with supported values 'off', 'auto', 'system',
'bernoulli' and 'random'. The default value is 'auto' which uses either
'bernoulli' (TABLESAMPLE method) or 'random' (for remote servers without
TABLESAMPLE support).
This commit is contained in:
Tomas Vondra
2022-12-30 23:14:53 +01:00
parent 02699bc1fd
commit 8ad51b5f44
7 changed files with 397 additions and 9 deletions
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15
contrib/postgres_fdw/postgres_fdw.h
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@ -134,6 +134,18 @@ typedef struct PgFdwConnState
AsyncRequest *pendingAreq; /* pending async request */
} PgFdwConnState;
/*
* Method used by ANALYZE to sample remote rows.
*/
typedef enum PgFdwSamplingMethod
{
ANALYZE_SAMPLE_OFF, /* no remote sampling */
ANALYZE_SAMPLE_AUTO, /* choose by server version */
ANALYZE_SAMPLE_RANDOM, /* remote random() */
ANALYZE_SAMPLE_SYSTEM, /* TABLESAMPLE system */
ANALYZE_SAMPLE_BERNOULLI /* TABLESAMPLE bernoulli */
} PgFdwSamplingMethod;
/* in postgres_fdw.c */
extern int set_transmission_modes(void);
extern void reset_transmission_modes(int nestlevel);
@ -211,7 +223,10 @@ extern void deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
List *returningList,
List **retrieved_attrs);
extern void deparseAnalyzeSizeSql(StringInfo buf, Relation rel);
extern void deparseAnalyzeTuplesSql(StringInfo buf, Relation rel);
extern void deparseAnalyzeSql(StringInfo buf, Relation rel,
PgFdwSamplingMethod sample_method,
double sample_frac,
List **retrieved_attrs);
extern void deparseTruncateSql(StringInfo buf,
List *rels,