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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 and
server OID, but this can lead to multiple connections when it's not
really necessary.  In particular, if all relevant users are mapped to
the public user mapping, then their connection options are certainly
the same, so one connection can be used for all of them.

While we're cleaning things up here, drop the "server" argument to
GetConnection(), which isn't really needed.  This saves a few cycles
because callers no longer have to look this up; the function itself
does, but only when establishing a new connection, not when reusing
an existing one.

Ashutosh Bapat, with a few small changes by me.
This commit is contained in:
Robert Haas 2016-01-28 12:05:19 -05:00
parent 80db1ca2d7
commit 96198d94cb
5 changed files with 26 additions and 34 deletions
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27
contrib/postgres_fdw/connection.c
View File

@ -24,9 +24,11 @@
/*
* Connection cache hash table entry
*
* The lookup key in this hash table is the foreign server OID plus the user
* mapping OID. (We use just one connection per user per foreign server,
* so that we can ensure all scans use the same snapshot during a query.)
* The lookup key in this hash table is the user mapping OID. We use just one
* connection per user mapping ID, which ensures that all the scans use the
* same snapshot during a query. Using the user mapping OID rather than
* the foreign server OID + user OID avoids creating multiple connections when
* the public user mapping applies to all user OIDs.
*
* The "conn" pointer can be NULL if we don't currently have a live connection.
* When we do have a connection, xact_depth tracks the current depth of
@ -35,11 +37,7 @@
* ourselves, so that rolling back a subtransaction will kill the right
* queries and not the wrong ones.
*/
typedef struct ConnCacheKey
{
Oid serverid; /* OID of foreign server */
Oid userid; /* OID of local user whose mapping we use */
} ConnCacheKey;
typedef Oid ConnCacheKey;
typedef struct ConnCacheEntry
{
@ -94,8 +92,7 @@ static void pgfdw_subxact_callback(SubXactEvent event,
* mid-transaction anyway.
*/
PGconn *
GetConnection(ForeignServer *server, UserMapping *user,
bool will_prep_stmt)
GetConnection(UserMapping *user, bool will_prep_stmt)
{
bool found;
ConnCacheEntry *entry;
@ -127,8 +124,7 @@ GetConnection(ForeignServer *server, UserMapping *user,
xact_got_connection = true;
/* Create hash key for the entry. Assume no pad bytes in key struct */
key.serverid = server->serverid;
key.userid = user->userid;
key = user->umid;
/*
* Find or create cached entry for requested connection.
@ -156,12 +152,15 @@ GetConnection(ForeignServer *server, UserMapping *user,
*/
if (entry->conn == NULL)
{
ForeignServer *server = GetForeignServer(user->serverid);
entry->xact_depth = 0; /* just to be sure */
entry->have_prep_stmt = false;
entry->have_error = false;
entry->conn = connect_pg_server(server, user);
elog(DEBUG3, "new postgres_fdw connection %p for server \"%s\"",
entry->conn, server->servername);
elog(DEBUG3, "new postgres_fdw connection %p for server \"%s\ (user mapping oid %d, userid %d)",
entry->conn, server->servername, user->umid, user->userid);
}
/*

28
contrib/postgres_fdw/postgres_fdw.c
View File

@ -1101,7 +1101,6 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
RangeTblEntry *rte;
Oid userid;
ForeignTable *table;
ForeignServer *server;
UserMapping *user;
int numParams;
int i;
@ -1129,14 +1128,13 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
/* Get info about foreign table. */
fsstate->rel = node->ss.ss_currentRelation;
table = GetForeignTable(RelationGetRelid(fsstate->rel));
server = GetForeignServer(table->serverid);
user = GetUserMapping(userid, server->serverid);
user = GetUserMapping(userid, table->serverid);
/*
* Get connection to the foreign server. Connection manager will
* establish new connection if necessary.
*/
fsstate->conn = GetConnection(server, user, false);
fsstate->conn = GetConnection(user, false);
/* Assign a unique ID for my cursor */
fsstate->cursor_number = GetCursorNumber(fsstate->conn);
@ -1503,7 +1501,6 @@ postgresBeginForeignModify(ModifyTableState *mtstate,
RangeTblEntry *rte;
Oid userid;
ForeignTable *table;
ForeignServer *server;
UserMapping *user;
AttrNumber n_params;
Oid typefnoid;
@ -1530,11 +1527,10 @@ postgresBeginForeignModify(ModifyTableState *mtstate,
/* Get info about foreign table. */
table = GetForeignTable(RelationGetRelid(rel));
server = GetForeignServer(table->serverid);
user = GetUserMapping(userid, server->serverid);
user = GetUserMapping(userid, table->serverid);
/* Open connection; report that we'll create a prepared statement. */
fmstate->conn = GetConnection(server, user, true);
fmstate->conn = GetConnection(user, true);
fmstate->p_name = NULL; /* prepared statement not made yet */
/* Deconstruct fdw_private data. */
@ -1988,7 +1984,7 @@ estimate_path_cost_size(PlannerInfo *root,
appendOrderByClause(&sql, root, baserel, pathkeys);
/* Get the remote estimate */
conn = GetConnection(fpinfo->server, fpinfo->user, false);
conn = GetConnection(fpinfo->user, false);
get_remote_estimate(sql.data, conn, &rows, &width,
&startup_cost, &total_cost);
ReleaseConnection(conn);
@ -2544,7 +2540,6 @@ postgresAnalyzeForeignTable(Relation relation,
BlockNumber *totalpages)
{
ForeignTable *table;
ForeignServer *server;
UserMapping *user;
PGconn *conn;
StringInfoData sql;
@ -2565,9 +2560,8 @@ postgresAnalyzeForeignTable(Relation relation,
* 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, server->serverid);
conn = GetConnection(server, user, false);
user = GetUserMapping(relation->rd_rel->relowner, table->serverid);
conn = GetConnection(user, false);
/*
* Construct command to get page count for relation.
@ -2626,7 +2620,6 @@ postgresAcquireSampleRowsFunc(Relation relation, int elevel,
{
PgFdwAnalyzeState astate;
ForeignTable *table;
ForeignServer *server;
UserMapping *user;
PGconn *conn;
unsigned int cursor_number;
@ -2657,9 +2650,8 @@ 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, server->serverid);
conn = GetConnection(server, user, false);
user = GetUserMapping(relation->rd_rel->relowner, table->serverid);
conn = GetConnection(user, false);
/*
* Construct cursor that retrieves whole rows from remote.
@ -2860,7 +2852,7 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
*/
server = GetForeignServer(serverOid);
mapping = GetUserMapping(GetUserId(), server->serverid);
conn = GetConnection(server, mapping, false);
conn = GetConnection(mapping, false);
/* Don't attempt to import collation if remote server hasn't got it */
if (PQserverVersion(conn) < 90100)

3
contrib/postgres_fdw/postgres_fdw.h
View File

@ -60,8 +60,7 @@ extern int set_transmission_modes(void);
extern void reset_transmission_modes(int nestlevel);
/* in connection.c */
extern PGconn *GetConnection(ForeignServer *server, UserMapping *user,
bool will_prep_stmt);
extern PGconn *GetConnection(UserMapping *user, bool will_prep_stmt);
extern void ReleaseConnection(PGconn *conn);
extern unsigned int GetCursorNumber(PGconn *conn);
extern unsigned int GetPrepStmtNumber(PGconn *conn);

1
src/backend/foreign/foreign.c
View File

@ -193,6 +193,7 @@ GetUserMapping(Oid userid, Oid serverid)
MappingUserName(userid))));
um = (UserMapping *) palloc(sizeof(UserMapping));
um->umid = HeapTupleGetOid(tp);
um->userid = userid;
um->serverid = serverid;

1
src/include/foreign/foreign.h
View File

@ -55,6 +55,7 @@ typedef struct ForeignServer
typedef struct UserMapping
{
Oid umid; /* Oid of user mapping */
Oid userid; /* local user Oid */
Oid serverid; /* server Oid */
List *options; /* useoptions as DefElem list */