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Commit96198d9

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Avoid multiple foreign server connections when all use same user mapping.
Previously, postgres_fdw's connection cache was keyed by user OID andserver OID, but this can lead to multiple connections when it's notreally necessary. In particular, if all relevant users are mapped tothe public user mapping, then their connection options are certainlythe same, so one connection can be used for all of them.While we're cleaning things up here, drop the "server" argument toGetConnection(), which isn't really needed. This saves a few cyclesbecause callers no longer have to look this up; the function itselfdoes, but only when establishing a new connection, not when reusingan existing one.Ashutosh Bapat, with a few small changes by me.
1 parent80db1ca commit96198d9

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5 files changed

+26
-34
lines changed

5 files changed

+26
-34
lines changed

‎contrib/postgres_fdw/connection.c

Lines changed: 13 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -24,9 +24,11 @@
2424
/*
2525
* Connection cache hash table entry
2626
*
27-
* The lookup key in this hash table is the foreign server OID plus the user
28-
* mapping OID. (We use just one connection per user per foreign server,
29-
* so that we can ensure all scans use the same snapshot during a query.)
27+
* The lookup key in this hash table is the user mapping OID. We use just one
28+
* connection per user mapping ID, which ensures that all the scans use the
29+
* same snapshot during a query. Using the user mapping OID rather than
30+
* the foreign server OID + user OID avoids creating multiple connections when
31+
* the public user mapping applies to all user OIDs.
3032
*
3133
* The "conn" pointer can be NULL if we don't currently have a live connection.
3234
* When we do have a connection, xact_depth tracks the current depth of
@@ -35,11 +37,7 @@
3537
* ourselves, so that rolling back a subtransaction will kill the right
3638
* queries and not the wrong ones.
3739
*/
38-
typedefstructConnCacheKey
39-
{
40-
Oidserverid;/* OID of foreign server */
41-
Oiduserid;/* OID of local user whose mapping we use */
42-
}ConnCacheKey;
40+
typedefOidConnCacheKey;
4341

4442
typedefstructConnCacheEntry
4543
{
@@ -94,8 +92,7 @@ static void pgfdw_subxact_callback(SubXactEvent event,
9492
* mid-transaction anyway.
9593
*/
9694
PGconn*
97-
GetConnection(ForeignServer*server,UserMapping*user,
98-
boolwill_prep_stmt)
95+
GetConnection(UserMapping*user,boolwill_prep_stmt)
9996
{
10097
boolfound;
10198
ConnCacheEntry*entry;
@@ -127,8 +124,7 @@ GetConnection(ForeignServer *server, UserMapping *user,
127124
xact_got_connection= true;
128125

129126
/* Create hash key for the entry. Assume no pad bytes in key struct */
130-
key.serverid=server->serverid;
131-
key.userid=user->userid;
127+
key=user->umid;
132128

133129
/*
134130
* Find or create cached entry for requested connection.
@@ -156,12 +152,15 @@ GetConnection(ForeignServer *server, UserMapping *user,
156152
*/
157153
if (entry->conn==NULL)
158154
{
155+
ForeignServer*server=GetForeignServer(user->serverid);
156+
159157
entry->xact_depth=0;/* just to be sure */
160158
entry->have_prep_stmt= false;
161159
entry->have_error= false;
162160
entry->conn=connect_pg_server(server,user);
163-
elog(DEBUG3,"new postgres_fdw connection %p for server \"%s\"",
164-
entry->conn,server->servername);
161+
162+
elog(DEBUG3,"new postgres_fdw connection %p for server \"%s\ (user mapping oid %d, userid %d)",
163+
entry->conn,server->servername,user->umid,user->userid);
165164
}
166165

167166
/*

‎contrib/postgres_fdw/postgres_fdw.c

Lines changed: 10 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -1101,7 +1101,6 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
11011101
RangeTblEntry*rte;
11021102
Oiduserid;
11031103
ForeignTable*table;
1104-
ForeignServer*server;
11051104
UserMapping*user;
11061105
intnumParams;
11071106
inti;
@@ -1129,14 +1128,13 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
11291128
/* Get info about foreign table. */
11301129
fsstate->rel=node->ss.ss_currentRelation;
11311130
table=GetForeignTable(RelationGetRelid(fsstate->rel));
1132-
server=GetForeignServer(table->serverid);
1133-
user=GetUserMapping(userid,server->serverid);
1131+
user=GetUserMapping(userid,table->serverid);
11341132

11351133
/*
11361134
* Get connection to the foreign server. Connection manager will
11371135
* establish new connection if necessary.
11381136
*/
1139-
fsstate->conn=GetConnection(server,user, false);
1137+
fsstate->conn=GetConnection(user, false);
11401138

11411139
/* Assign a unique ID for my cursor */
11421140
fsstate->cursor_number=GetCursorNumber(fsstate->conn);
@@ -1503,7 +1501,6 @@ postgresBeginForeignModify(ModifyTableState *mtstate,
15031501
RangeTblEntry*rte;
15041502
Oiduserid;
15051503
ForeignTable*table;
1506-
ForeignServer*server;
15071504
UserMapping*user;
15081505
AttrNumbern_params;
15091506
Oidtypefnoid;
@@ -1530,11 +1527,10 @@ postgresBeginForeignModify(ModifyTableState *mtstate,
15301527

15311528
/* Get info about foreign table. */
15321529
table=GetForeignTable(RelationGetRelid(rel));
1533-
server=GetForeignServer(table->serverid);
1534-
user=GetUserMapping(userid,server->serverid);
1530+
user=GetUserMapping(userid,table->serverid);
15351531

15361532
/* Open connection; report that we'll create a prepared statement. */
1537-
fmstate->conn=GetConnection(server,user, true);
1533+
fmstate->conn=GetConnection(user, true);
15381534
fmstate->p_name=NULL;/* prepared statement not made yet */
15391535

15401536
/* Deconstruct fdw_private data. */
@@ -1988,7 +1984,7 @@ estimate_path_cost_size(PlannerInfo *root,
19881984
appendOrderByClause(&sql,root,baserel,pathkeys);
19891985

19901986
/* Get the remote estimate */
1991-
conn=GetConnection(fpinfo->server,fpinfo->user, false);
1987+
conn=GetConnection(fpinfo->user, false);
19921988
get_remote_estimate(sql.data,conn,&rows,&width,
19931989
&startup_cost,&total_cost);
19941990
ReleaseConnection(conn);
@@ -2544,7 +2540,6 @@ postgresAnalyzeForeignTable(Relation relation,
25442540
BlockNumber*totalpages)
25452541
{
25462542
ForeignTable*table;
2547-
ForeignServer*server;
25482543
UserMapping*user;
25492544
PGconn*conn;
25502545
StringInfoDatasql;
@@ -2565,9 +2560,8 @@ postgresAnalyzeForeignTable(Relation relation,
25652560
* owner, even if the ANALYZE was started by some other user.
25662561
*/
25672562
table=GetForeignTable(RelationGetRelid(relation));
2568-
server=GetForeignServer(table->serverid);
2569-
user=GetUserMapping(relation->rd_rel->relowner,server->serverid);
2570-
conn=GetConnection(server,user, false);
2563+
user=GetUserMapping(relation->rd_rel->relowner,table->serverid);
2564+
conn=GetConnection(user, false);
25712565

25722566
/*
25732567
* Construct command to get page count for relation.
@@ -2626,7 +2620,6 @@ postgresAcquireSampleRowsFunc(Relation relation, int elevel,
26262620
{
26272621
PgFdwAnalyzeStateastate;
26282622
ForeignTable*table;
2629-
ForeignServer*server;
26302623
UserMapping*user;
26312624
PGconn*conn;
26322625
unsignedintcursor_number;
@@ -2657,9 +2650,8 @@ postgresAcquireSampleRowsFunc(Relation relation, int elevel,
26572650
* owner, even if the ANALYZE was started by some other user.
26582651
*/
26592652
table=GetForeignTable(RelationGetRelid(relation));
2660-
server=GetForeignServer(table->serverid);
2661-
user=GetUserMapping(relation->rd_rel->relowner,server->serverid);
2662-
conn=GetConnection(server,user, false);
2653+
user=GetUserMapping(relation->rd_rel->relowner,table->serverid);
2654+
conn=GetConnection(user, false);
26632655

26642656
/*
26652657
* Construct cursor that retrieves whole rows from remote.
@@ -2860,7 +2852,7 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
28602852
*/
28612853
server=GetForeignServer(serverOid);
28622854
mapping=GetUserMapping(GetUserId(),server->serverid);
2863-
conn=GetConnection(server,mapping, false);
2855+
conn=GetConnection(mapping, false);
28642856

28652857
/* Don't attempt to import collation if remote server hasn't got it */
28662858
if (PQserverVersion(conn)<90100)

‎contrib/postgres_fdw/postgres_fdw.h

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -60,8 +60,7 @@ extern intset_transmission_modes(void);
6060
externvoidreset_transmission_modes(intnestlevel);
6161

6262
/* in connection.c */
63-
externPGconn*GetConnection(ForeignServer*server,UserMapping*user,
64-
boolwill_prep_stmt);
63+
externPGconn*GetConnection(UserMapping*user,boolwill_prep_stmt);
6564
externvoidReleaseConnection(PGconn*conn);
6665
externunsignedintGetCursorNumber(PGconn*conn);
6766
externunsignedintGetPrepStmtNumber(PGconn*conn);

‎src/backend/foreign/foreign.c

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -193,6 +193,7 @@ GetUserMapping(Oid userid, Oid serverid)
193193
MappingUserName(userid))));
194194

195195
um= (UserMapping*)palloc(sizeof(UserMapping));
196+
um->umid=HeapTupleGetOid(tp);
196197
um->userid=userid;
197198
um->serverid=serverid;
198199

‎src/include/foreign/foreign.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -55,6 +55,7 @@ typedef struct ForeignServer
5555

5656
typedefstructUserMapping
5757
{
58+
Oidumid;/* Oid of user mapping */
5859
Oiduserid;/* local user Oid */
5960
Oidserverid;/* server Oid */
6061
List*options;/* useoptions as DefElem list */

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