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Improve connection-failure error handling in contrib/postgres_fdw.

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postgres_fdw tended to say "unknown error" if it tried to execute a command
on an already-dead connection, because some paths in libpq just return a
null PGresult for such cases.  Out-of-memory might result in that, too.
To fix, pass the PGconn to pgfdw_report_error, and look at its
PQerrorMessage() string if we can't get anything out of the PGresult.

Also, fix the transaction-exit logic to reliably drop a dead connection.
It was attempting to do that already, but it assumed that only connection
cache entries with xact_depth > 0 needed to be examined.  The folly in that
is that if we fail while issuing START TRANSACTION, we'll not have bumped
xact_depth.  (At least for the case I was testing, this fix masks the
other problem; but it still seems like a good idea to have the PGconn
fallback logic.)

Per investigation of bug #9087 from Craig Lucas.  Backpatch to 9.3 where
this code was introduced.
This commit is contained in:
Tom Lane
2014-02-03 21:30:02 -05:00
parent 489e6ac5a1
commit 00d4f2af8b
3 changed files with 98 additions and 83 deletions
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26
contrib/postgres_fdw/postgres_fdw.c
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@ -1040,7 +1040,7 @@ postgresReScanForeignScan(ForeignScanState *node)
*/
res = PQexec(fsstate->conn, sql);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(ERROR, res, true, sql);
pgfdw_report_error(ERROR, res, fsstate->conn, true, sql);
PQclear(res);
/* Now force a fresh FETCH. */
@ -1374,7 +1374,7 @@ postgresExecForeignInsert(EState *estate,
0);
if (PQresultStatus(res) !=
(fmstate->has_returning ? PGRES_TUPLES_OK : PGRES_COMMAND_OK))
pgfdw_report_error(ERROR, res, true, fmstate->query);
pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
/* Check number of rows affected, and fetch RETURNING tuple if any */
if (fmstate->has_returning)
@ -1444,7 +1444,7 @@ postgresExecForeignUpdate(EState *estate,
0);
if (PQresultStatus(res) !=
(fmstate->has_returning ? PGRES_TUPLES_OK : PGRES_COMMAND_OK))
pgfdw_report_error(ERROR, res, true, fmstate->query);
pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
/* Check number of rows affected, and fetch RETURNING tuple if any */
if (fmstate->has_returning)
@ -1514,7 +1514,7 @@ postgresExecForeignDelete(EState *estate,
0);
if (PQresultStatus(res) !=
(fmstate->has_returning ? PGRES_TUPLES_OK : PGRES_COMMAND_OK))
pgfdw_report_error(ERROR, res, true, fmstate->query);
pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
/* Check number of rows affected, and fetch RETURNING tuple if any */
if (fmstate->has_returning)
@ -1563,7 +1563,7 @@ postgresEndForeignModify(EState *estate,
*/
res = PQexec(fmstate->conn, sql);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(ERROR, res, true, sql);
pgfdw_report_error(ERROR, res, fmstate->conn, true, sql);
PQclear(res);
fmstate->p_name = NULL;
}
@ -1800,7 +1800,7 @@ get_remote_estimate(const char *sql, PGconn *conn,
*/
res = PQexec(conn, sql);
if (PQresultStatus(res) != PGRES_TUPLES_OK)
pgfdw_report_error(ERROR, res, false, sql);
pgfdw_report_error(ERROR, res, conn, false, sql);
/*
* Extract cost numbers for topmost plan node. Note we search for a
@ -1934,7 +1934,7 @@ create_cursor(ForeignScanState *node)
res = PQexecParams(conn, buf.data, numParams, NULL, values,
NULL, NULL, 0);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(ERROR, res, true, fsstate->query);
pgfdw_report_error(ERROR, res, conn, true, fsstate->query);
PQclear(res);
/* Mark the cursor as created, and show no tuples have been retrieved */
@ -1985,7 +1985,7 @@ fetch_more_data(ForeignScanState *node)
res = PQexec(conn, sql);
/* On error, report the original query, not the FETCH. */
if (PQresultStatus(res) != PGRES_TUPLES_OK)
pgfdw_report_error(ERROR, res, false, fsstate->query);
pgfdw_report_error(ERROR, res, conn, false, fsstate->query);
/* Convert the data into HeapTuples */
numrows = PQntuples(res);
@ -2091,7 +2091,7 @@ close_cursor(PGconn *conn, unsigned int cursor_number)
*/
res = PQexec(conn, sql);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(ERROR, res, true, sql);
pgfdw_report_error(ERROR, res, conn, true, sql);
PQclear(res);
}
@ -2128,7 +2128,7 @@ prepare_foreign_modify(PgFdwModifyState *fmstate)
NULL);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(ERROR, res, true, fmstate->query);
pgfdw_report_error(ERROR, res, fmstate->conn, true, fmstate->query);
PQclear(res);
/* This action shows that the prepare has been done. */
@ -2278,7 +2278,7 @@ postgresAnalyzeForeignTable(Relation relation,
{
res = PQexec(conn, sql.data);
if (PQresultStatus(res) != PGRES_TUPLES_OK)
pgfdw_report_error(ERROR, res, false, sql.data);
pgfdw_report_error(ERROR, res, conn, false, sql.data);
if (PQntuples(res) != 1 || PQnfields(res) != 1)
elog(ERROR, "unexpected result from deparseAnalyzeSizeSql query");
@ -2372,7 +2372,7 @@ postgresAcquireSampleRowsFunc(Relation relation, int elevel,
{
res = PQexec(conn, sql.data);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(ERROR, res, false, sql.data);
pgfdw_report_error(ERROR, res, conn, false, sql.data);
PQclear(res);
res = NULL;
@ -2403,7 +2403,7 @@ postgresAcquireSampleRowsFunc(Relation relation, int elevel,
res = PQexec(conn, fetch_sql);
/* On error, report the original query, not the FETCH. */
if (PQresultStatus(res) != PGRES_TUPLES_OK)
pgfdw_report_error(ERROR, res, false, sql.data);
pgfdw_report_error(ERROR, res, conn, false, sql.data);
/* Process whatever we got. */
numrows = PQntuples(res);