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postgres_fdw: Allow fetch_size to be set per-table or per-server.

Browse Source 
The default fetch size of 100 rows might not be right in every
environment, so allow users to configure it.

Corey Huinker, reviewed by Kyotaro Horiguchi, Andres Freund, and me.
pull/10/merge
Robert Haas 10 years ago
parent e6ecc93a17
commit dc203dc3ac
6 changed files with 180 additions and 17 deletions
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
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  1. 60
      contrib/postgres_fdw/expected/postgres_fdw.out
  2. 14
      contrib/postgres_fdw/option.c
  3. 50
      contrib/postgres_fdw/postgres_fdw.c
  4. 2
      contrib/postgres_fdw/postgres_fdw.h
  5. 44
      contrib/postgres_fdw/sql/postgres_fdw.sql
  6. 27
      doc/src/sgml/postgres-fdw.sgml

60
contrib/postgres_fdw/expected/postgres_fdw.out
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@ -3951,3 +3951,63 @@ QUERY: CREATE FOREIGN TABLE t5 (
OPTIONS (schema_name 'import_source', table_name 't5');
CONTEXT: importing foreign table "t5"
ROLLBACK;
BEGIN;
CREATE SERVER fetch101 FOREIGN DATA WRAPPER postgres_fdw OPTIONS( fetch_size '101' );
SELECT count(*)
FROM pg_foreign_server
WHERE srvname = 'fetch101'
AND srvoptions @> array['fetch_size=101'];
count
-------
1
(1 row)
ALTER SERVER fetch101 OPTIONS( SET fetch_size '202' );
SELECT count(*)
FROM pg_foreign_server
WHERE srvname = 'fetch101'
AND srvoptions @> array['fetch_size=101'];
count
-------
0
(1 row)
SELECT count(*)
FROM pg_foreign_server
WHERE srvname = 'fetch101'
AND srvoptions @> array['fetch_size=202'];
count
-------
1
(1 row)
CREATE FOREIGN TABLE table30000 ( x int ) SERVER fetch101 OPTIONS ( fetch_size '30000' );
SELECT COUNT(*)
FROM pg_foreign_table
WHERE ftrelid = 'table30000'::regclass
AND ftoptions @> array['fetch_size=30000'];
count
-------
1
(1 row)
ALTER FOREIGN TABLE table30000 OPTIONS ( SET fetch_size '60000');
SELECT COUNT(*)
FROM pg_foreign_table
WHERE ftrelid = 'table30000'::regclass
AND ftoptions @> array['fetch_size=30000'];
count
-------
0
(1 row)
SELECT COUNT(*)
FROM pg_foreign_table
WHERE ftrelid = 'table30000'::regclass
AND ftoptions @> array['fetch_size=60000'];
count
-------
1
(1 row)
ROLLBACK;

14
contrib/postgres_fdw/option.c
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@ -131,6 +131,17 @@ postgres_fdw_validator(PG_FUNCTION_ARGS)
/* check list syntax, warn about uninstalled extensions */
(void) ExtractExtensionList(defGetString(def), true);
}
else if (strcmp(def->defname, "fetch_size") == 0)
{
int fetch_size;
fetch_size = strtol(defGetString(def), NULL,10);
if (fetch_size <= 0)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("%s requires a non-negative integer value",
def->defname)));
}
}
PG_RETURN_VOID();
@ -162,6 +173,9 @@ InitPgFdwOptions(void)
/* updatable is available on both server and table */
{"updatable", ForeignServerRelationId, false},
{"updatable", ForeignTableRelationId, false},
/* fetch_size is available on both server and table */
{"fetch_size", ForeignServerRelationId, false},
{"fetch_size", ForeignTableRelationId, false},
{NULL, InvalidOid, false}
};

50
contrib/postgres_fdw/postgres_fdw.c
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@ -68,7 +68,9 @@ enum FdwScanPrivateIndex
/* SQL statement to execute remotely (as a String node) */
FdwScanPrivateSelectSql,
/* Integer list of attribute numbers retrieved by the SELECT */
FdwScanPrivateRetrievedAttrs
FdwScanPrivateRetrievedAttrs,
/* Integer representing the desired fetch_size */
FdwScanPrivateFetchSize
};
/*
@ -126,6 +128,8 @@ typedef struct PgFdwScanState
/* working memory contexts */
MemoryContext batch_cxt; /* context holding current batch of tuples */
MemoryContext temp_cxt; /* context for per-tuple temporary data */
int fetch_size; /* number of tuples per fetch */
} PgFdwScanState;
/*
@ -380,6 +384,7 @@ postgresGetForeignRelSize(PlannerInfo *root,
fpinfo->fdw_startup_cost = DEFAULT_FDW_STARTUP_COST;
fpinfo->fdw_tuple_cost = DEFAULT_FDW_TUPLE_COST;
fpinfo->shippable_extensions = NIL;
fpinfo->fetch_size = 100;
foreach(lc, fpinfo->server->options)
{
@ -394,16 +399,17 @@ postgresGetForeignRelSize(PlannerInfo *root,
else if (strcmp(def->defname, "extensions") == 0)
fpinfo->shippable_extensions =
ExtractExtensionList(defGetString(def), false);
else if (strcmp(def->defname, "fetch_size") == 0)
fpinfo->fetch_size = strtol(defGetString(def), NULL,10);
}
foreach(lc, fpinfo->table->options)
{
DefElem *def = (DefElem *) lfirst(lc);
if (strcmp(def->defname, "use_remote_estimate") == 0)
{
fpinfo->use_remote_estimate = defGetBoolean(def);
break; /* only need the one value */
}
else if (strcmp(def->defname, "fetch_size") == 0)
fpinfo->fetch_size = strtol(defGetString(def), NULL,10);
}
/*
@ -1012,6 +1018,9 @@ postgresGetForeignPlan(PlannerInfo *root,
*/
fdw_private = list_make2(makeString(sql.data),
retrieved_attrs);
fdw_private = list_make3(makeString(sql.data),
retrieved_attrs,
makeInteger(fpinfo->fetch_size));
/*
* Create the ForeignScan node from target list, filtering expressions,
@ -1088,6 +1097,8 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
FdwScanPrivateSelectSql));
fsstate->retrieved_attrs = (List *) list_nth(fsplan->fdw_private,
FdwScanPrivateRetrievedAttrs);
fsstate->fetch_size = intVal(list_nth(fsplan->fdw_private,
FdwScanPrivateFetchSize));
/* Create contexts for batches of tuples and per-tuple temp workspace. */
fsstate->batch_cxt = AllocSetContextCreate(estate->es_query_cxt,
@ -2214,15 +2225,11 @@ fetch_more_data(ForeignScanState *node)
{
PGconn *conn = fsstate->conn;
char sql[64];
int fetch_size;
int numrows;
int i;
/* The fetch size is arbitrary, but shouldn't be enormous. */
fetch_size = 100;
snprintf(sql, sizeof(sql), "FETCH %d FROM c%u",
fetch_size, fsstate->cursor_number);
fsstate->fetch_size, fsstate->cursor_number);
res = PQexec(conn, sql);
/* On error, report the original query, not the FETCH. */
@ -2250,7 +2257,7 @@ fetch_more_data(ForeignScanState *node)
fsstate->fetch_ct_2++;
/* Must be EOF if we didn't get as many tuples as we asked for. */
fsstate->eof_reached = (numrows < fetch_size);
fsstate->eof_reached = (numrows < fsstate->fetch_size);
PQclear(res);
res = NULL;
@ -2563,6 +2570,7 @@ postgresAcquireSampleRowsFunc(Relation relation, int elevel,
{
PgFdwAnalyzeState astate;
ForeignTable *table;
ForeignServer *server;
UserMapping *user;
PGconn *conn;
unsigned int cursor_number;
@ -2593,6 +2601,7 @@ postgresAcquireSampleRowsFunc(Relation relation, int elevel,
* owner, even if the ANALYZE was started by some other user.
*/
table = GetForeignTable(RelationGetRelid(relation));
server = GetForeignServer(table->serverid);
user = GetUserMapping(relation->rd_rel->relowner, table->serverid);
conn = GetConnection(user, false);
@ -2620,6 +2629,7 @@ postgresAcquireSampleRowsFunc(Relation relation, int elevel,
int fetch_size;
int numrows;
int i;
ListCell *lc;
/* Allow users to cancel long query */
CHECK_FOR_INTERRUPTS();
@ -2632,6 +2642,26 @@ postgresAcquireSampleRowsFunc(Relation relation, int elevel,
/* The fetch size is arbitrary, but shouldn't be enormous. */
fetch_size = 100;
foreach(lc, server->options)
{
DefElem *def = (DefElem *) lfirst(lc);
if (strcmp(def->defname, "fetch_size") == 0)
{
fetch_size = strtol(defGetString(def), NULL,10);
break;
}
}
foreach(lc, table->options)
{
DefElem *def = (DefElem *) lfirst(lc);
if (strcmp(def->defname, "fetch_size") == 0)
{
fetch_size = strtol(defGetString(def), NULL,10);
break;
}
}
/* Fetch some rows */
snprintf(fetch_sql, sizeof(fetch_sql), "FETCH %d FROM c%u",

2
contrib/postgres_fdw/postgres_fdw.h
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@ -53,6 +53,8 @@ typedef struct PgFdwRelationInfo
ForeignTable *table;
ForeignServer *server;
UserMapping *user; /* only set in use_remote_estimate mode */
int fetch_size; /* fetch size for this remote table */
} PgFdwRelationInfo;
/* in postgres_fdw.c */

44
contrib/postgres_fdw/sql/postgres_fdw.sql
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@ -919,4 +919,48 @@ BEGIN;
DROP TYPE "Colors" CASCADE;
IMPORT FOREIGN SCHEMA import_source LIMIT TO (t5)
FROM SERVER loopback INTO import_dest5; -- ERROR
ROLLBACK;
BEGIN;
CREATE SERVER fetch101 FOREIGN DATA WRAPPER postgres_fdw OPTIONS( fetch_size '101' );
SELECT count(*)
FROM pg_foreign_server
WHERE srvname = 'fetch101'
AND srvoptions @> array['fetch_size=101'];
ALTER SERVER fetch101 OPTIONS( SET fetch_size '202' );
SELECT count(*)
FROM pg_foreign_server
WHERE srvname = 'fetch101'
AND srvoptions @> array['fetch_size=101'];
SELECT count(*)
FROM pg_foreign_server
WHERE srvname = 'fetch101'
AND srvoptions @> array['fetch_size=202'];
CREATE FOREIGN TABLE table30000 ( x int ) SERVER fetch101 OPTIONS ( fetch_size '30000' );
SELECT COUNT(*)
FROM pg_foreign_table
WHERE ftrelid = 'table30000'::regclass
AND ftoptions @> array['fetch_size=30000'];
ALTER FOREIGN TABLE table30000 OPTIONS ( SET fetch_size '60000');
SELECT COUNT(*)
FROM pg_foreign_table
WHERE ftrelid = 'table30000'::regclass
AND ftoptions @> array['fetch_size=30000'];
SELECT COUNT(*)
FROM pg_foreign_table
WHERE ftrelid = 'table30000'::regclass
AND ftoptions @> array['fetch_size=60000'];
ROLLBACK;

27
doc/src/sgml/postgres-fdw.sgml
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@ -290,17 +290,30 @@
be considered shippable to the remote server.
This option can only be specified for foreign servers, not per-table.
</para>
<para>
When using the <literal>extensions</literal> option, <emphasis>it is the
user's responsibility</> that the listed extensions exist and behave
identically on both the local and remote servers. Otherwise, remote
queries may fail or behave unexpectedly.
</para>
</listitem>
</varlistentry>
</variablelist>
<varlistentry>
<term><literal>fetch_size</literal></term>
<listitem>
<para>
This option specifies the number of rows <filename>postgres_fdw</>
should get in each fetch operation. It can be specified for a foreign
table or a foreign server. The option specified on a table overrides
an option specified for the server.
The default is <literal>100</>.
</para>
</listitem>
</varlistentry>
<para>
When using the <literal>extensions</literal> option, <emphasis>it is the
user's responsibility</> that the listed extensions exist and behave
identically on both the local and remote servers. Otherwise, remote
queries may fail or behave unexpectedly.
</para>
</variablelist>
</sect3>

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