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Make dblink interruptible, via new libpqsrv APIs.

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This replaces dblink's blocking libpq calls, allowing cancellation and
allowing DROP DATABASE (of a database not involved in the query).  Apart
from explicit dblink_cancel_query() calls, dblink still doesn't cancel
the remote side.  The replacement for the blocking calls consists of
new, general-purpose query execution wrappers in the libpqsrv facility.
Out-of-tree extensions should adopt these.  Use them in postgres_fdw,
replacing a local implementation from which the libpqsrv implementation
derives.  This is a bug fix for dblink.  Code inspection identified the
bug at least thirteen years ago, but user complaints have not appeared.
Hence, no back-patch for now.

Discussion: https://postgr.es/m/20231122012945.74@rfd.leadboat.com
This commit is contained in:
Noah Misch
2024-01-08 11:39:56 -08:00
parent 0efc831847
commit d3c5f37dd5
8 changed files with 180 additions and 95 deletions
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88
contrib/postgres_fdw/connection.c
View File

@ -187,6 +187,10 @@ GetConnection(UserMapping *user, bool will_prep_stmt, PgFdwConnState **state)
{
HASHCTL ctl;
if (pgfdw_we_get_result == 0)
pgfdw_we_get_result =
WaitEventExtensionNew("PostgresFdwGetResult");
ctl.keysize = sizeof(ConnCacheKey);
ctl.entrysize = sizeof(ConnCacheEntry);
ConnectionHash = hash_create("postgres_fdw connections", 8,
@ -716,7 +720,7 @@ do_sql_command_end(PGconn *conn, const char *sql, bool consume_input)
*/
if (consume_input && !PQconsumeInput(conn))
pgfdw_report_error(ERROR, NULL, conn, false, sql);
res = pgfdw_get_result(conn, sql);
res = pgfdw_get_result(conn);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(ERROR, res, conn, true, sql);
PQclear(res);
@ -819,7 +823,9 @@ GetPrepStmtNumber(PGconn *conn)
/*
* Submit a query and wait for the result.
*
* This function is interruptible by signals.
* Since we don't use non-blocking mode, this can't process interrupts while
* pushing the query text to the server. That risk is relatively small, so we
* ignore that for now.
*
* Caller is responsible for the error handling on the result.
*/
@ -830,81 +836,20 @@ pgfdw_exec_query(PGconn *conn, const char *query, PgFdwConnState *state)
if (state && state->pendingAreq)
process_pending_request(state->pendingAreq);
/*
* Submit a query. Since we don't use non-blocking mode, this also can
* block. But its risk is relatively small, so we ignore that for now.
*/
if (!PQsendQuery(conn, query))
pgfdw_report_error(ERROR, NULL, conn, false, query);
/* Wait for the result. */
return pgfdw_get_result(conn, query);
return NULL;
return pgfdw_get_result(conn);
}
/*
* Wait for the result from a prior asynchronous execution function call.
*
* This function offers quick responsiveness by checking for any interruptions.
*
* This function emulates PQexec()'s behavior of returning the last result
* when there are many.
* Wrap libpqsrv_get_result_last(), adding wait event.
*
* Caller is responsible for the error handling on the result.
*/
PGresult *
pgfdw_get_result(PGconn *conn, const char *query)
pgfdw_get_result(PGconn *conn)
{
PGresult *volatile last_res = NULL;
/* In what follows, do not leak any PGresults on an error. */
PG_TRY();
{
for (;;)
{
PGresult *res;
while (PQisBusy(conn))
{
int wc;
/* first time, allocate or get the custom wait event */
if (pgfdw_we_get_result == 0)
pgfdw_we_get_result = WaitEventExtensionNew("PostgresFdwGetResult");
/* Sleep until there's something to do */
wc = WaitLatchOrSocket(MyLatch,
WL_LATCH_SET | WL_SOCKET_READABLE |
WL_EXIT_ON_PM_DEATH,
PQsocket(conn),
-1L, pgfdw_we_get_result);
ResetLatch(MyLatch);
CHECK_FOR_INTERRUPTS();
/* Data available in socket? */
if (wc & WL_SOCKET_READABLE)
{
if (!PQconsumeInput(conn))
pgfdw_report_error(ERROR, NULL, conn, false, query);
}
}
res = PQgetResult(conn);
if (res == NULL)
break; /* query is complete */
PQclear(last_res);
last_res = res;
}
}
PG_CATCH();
{
PQclear(last_res);
PG_RE_THROW();
}
PG_END_TRY();
return last_res;
return libpqsrv_get_result_last(conn, pgfdw_we_get_result);
}
/*
@ -945,8 +890,8 @@ pgfdw_report_error(int elevel, PGresult *res, PGconn *conn,
/*
* If we don't get a message from the PGresult, try the PGconn. This
* is needed because for connection-level failures, PQexec may just
* return NULL, not a PGresult at all.
* is needed because for connection-level failures, PQgetResult may
* just return NULL, not a PGresult at all.
*/
if (message_primary == NULL)
message_primary = pchomp(PQerrorMessage(conn));
@ -1046,7 +991,8 @@ pgfdw_xact_callback(XactEvent event, void *arg)
*/
if (entry->have_prep_stmt && entry->have_error)
{
res = PQexec(entry->conn, "DEALLOCATE ALL");
res = pgfdw_exec_query(entry->conn, "DEALLOCATE ALL",
NULL);
PQclear(res);
}
entry->have_prep_stmt = false;

2
contrib/postgres_fdw/deparse.c
View File

@ -3815,7 +3815,7 @@ appendOrderBySuffix(Oid sortop, Oid sortcoltype, bool nulls_first,
* Print the representation of a parameter to be sent to the remote side.
*
* Note: we always label the Param's type explicitly rather than relying on
* transmitting a numeric type OID in PQexecParams(). This allows us to
* transmitting a numeric type OID in PQsendQueryParams(). This allows us to
* avoid assuming that types have the same OIDs on the remote side as they
* do locally --- they need only have the same names.
*/

10
contrib/postgres_fdw/postgres_fdw.c
View File

@ -3760,7 +3760,7 @@ create_cursor(ForeignScanState *node)
* We don't use a PG_TRY block here, so be careful not to throw error
* without releasing the PGresult.
*/
res = pgfdw_get_result(conn, buf.data);
res = pgfdw_get_result(conn);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(ERROR, res, conn, true, fsstate->query);
PQclear(res);
@ -3810,7 +3810,7 @@ fetch_more_data(ForeignScanState *node)
* The query was already sent by an earlier call to
* fetch_more_data_begin. So now we just fetch the result.
*/
res = pgfdw_get_result(conn, fsstate->query);
res = pgfdw_get_result(conn);
/* On error, report the original query, not the FETCH. */
if (PQresultStatus(res) != PGRES_TUPLES_OK)
pgfdw_report_error(ERROR, res, conn, false, fsstate->query);
@ -4159,7 +4159,7 @@ execute_foreign_modify(EState *estate,
* We don't use a PG_TRY block here, so be careful not to throw error
* without releasing the PGresult.
*/
res = pgfdw_get_result(fmstate->conn, fmstate->query);
res = pgfdw_get_result(fmstate->conn);
if (PQresultStatus(res) !=
(fmstate->has_returning ? PGRES_TUPLES_OK : PGRES_COMMAND_OK))
pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
@ -4229,7 +4229,7 @@ prepare_foreign_modify(PgFdwModifyState *fmstate)
* We don't use a PG_TRY block here, so be careful not to throw error
* without releasing the PGresult.
*/
res = pgfdw_get_result(fmstate->conn, fmstate->query);
res = pgfdw_get_result(fmstate->conn);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
PQclear(res);
@ -4571,7 +4571,7 @@ execute_dml_stmt(ForeignScanState *node)
* We don't use a PG_TRY block here, so be careful not to throw error
* without releasing the PGresult.
*/
dmstate->result = pgfdw_get_result(dmstate->conn, dmstate->query);
dmstate->result = pgfdw_get_result(dmstate->conn);
if (PQresultStatus(dmstate->result) !=
(dmstate->has_returning ? PGRES_TUPLES_OK : PGRES_COMMAND_OK))
pgfdw_report_error(ERROR, dmstate->result, dmstate->conn, true,

2
contrib/postgres_fdw/postgres_fdw.h
View File

@ -162,7 +162,7 @@ extern void ReleaseConnection(PGconn *conn);
extern unsigned int GetCursorNumber(PGconn *conn);
extern unsigned int GetPrepStmtNumber(PGconn *conn);
extern void do_sql_command(PGconn *conn, const char *sql);
extern PGresult *pgfdw_get_result(PGconn *conn, const char *query);
extern PGresult *pgfdw_get_result(PGconn *conn);
extern PGresult *pgfdw_exec_query(PGconn *conn, const char *query,
PgFdwConnState *state);
extern void pgfdw_report_error(int elevel, PGresult *res, PGconn *conn,