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Make dblink try harder to form useful error messages

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When libpq encounters a connection-level error, e.g. runs out of memory
while forming a result, there will be no error associated with PGresult,
but a message will be placed into PGconn's error buffer. postgres_fdw
takes care to use the PGconn error message when PGresult does not have
one, but dblink has been negligent in that regard. Modify dblink to mirror
what postgres_fdw has been doing.

Back-patch to all supported branches.

Author: Joe Conway
Reviewed-By: Tom Lane
Discussion: https://postgr.es/m/02fa2d90-2efd-00bc-fefc-c23c00eb671e%40joeconway.com
This commit is contained in:
Joe Conway 2016-12-22 09:47:25 -08:00
parent bd46cce214
commit 9b8507bfae
1 changed files with 22 additions and 9 deletions
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31
contrib/dblink/dblink.c
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@ -113,7 +113,8 @@ static Relation get_rel_from_relname(text *relname_text, LOCKMODE lockmode, AclM
static char *generate_relation_name(Relation rel);
static void dblink_connstr_check(const char *connstr);
static void dblink_security_check(PGconn *conn, remoteConn *rconn);
static void dblink_res_error(const char *conname, PGresult *res, const char *dblink_context_msg, bool fail);
static void dblink_res_error(PGconn *conn, const char *conname, PGresult *res,
const char *dblink_context_msg, bool fail);
static char *get_connect_string(const char *servername);
static char *escape_param_str(const char *from);
static void validate_pkattnums(Relation rel,
@ -428,7 +429,7 @@ dblink_open(PG_FUNCTION_ARGS)
res = PQexec(conn, buf.data);
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
dblink_res_error(conname, res, "could not open cursor", fail);
dblink_res_error(conn, conname, res, "could not open cursor", fail);
PG_RETURN_TEXT_P(cstring_to_text("ERROR"));
}
@ -497,7 +498,7 @@ dblink_close(PG_FUNCTION_ARGS)
res = PQexec(conn, buf.data);
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
dblink_res_error(conname, res, "could not close cursor", fail);
dblink_res_error(conn, conname, res, "could not close cursor", fail);
PG_RETURN_TEXT_P(cstring_to_text("ERROR"));
}
@ -600,7 +601,8 @@ dblink_fetch(PG_FUNCTION_ARGS)
(PQresultStatus(res) != PGRES_COMMAND_OK &&
PQresultStatus(res) != PGRES_TUPLES_OK))
{
dblink_res_error(conname, res, "could not fetch from cursor", fail);
dblink_res_error(conn, conname, res,
"could not fetch from cursor", fail);
return (Datum) 0;
}
else if (PQresultStatus(res) == PGRES_COMMAND_OK)
@ -751,8 +753,8 @@ dblink_record_internal(FunctionCallInfo fcinfo, bool is_async)
if (PQresultStatus(res) != PGRES_COMMAND_OK &&
PQresultStatus(res) != PGRES_TUPLES_OK)
{
dblink_res_error(conname, res, "could not execute query",
fail);
dblink_res_error(conn, conname, res,
"could not execute query", fail);
/* if fail isn't set, we'll return an empty query result */
}
else
@ -999,7 +1001,8 @@ materializeQueryResult(FunctionCallInfo fcinfo,
PGresult *res1 = res;
res = NULL;
dblink_res_error(conname, res1, "could not execute query", fail);
dblink_res_error(conn, conname, res1,
"could not execute query", fail);
/* if fail isn't set, we'll return an empty query result */
}
else if (PQresultStatus(res) == PGRES_COMMAND_OK)
@ -1434,7 +1437,8 @@ dblink_exec(PG_FUNCTION_ARGS)
(PQresultStatus(res) != PGRES_COMMAND_OK &&
PQresultStatus(res) != PGRES_TUPLES_OK))
{
dblink_res_error(conname, res, "could not execute command", fail);
dblink_res_error(conn, conname, res,
"could not execute command", fail);
/*
* and save a copy of the command status string to return as our
@ -2668,7 +2672,8 @@ dblink_connstr_check(const char *connstr)
}
static void
dblink_res_error(const char *conname, PGresult *res, const char *dblink_context_msg, bool fail)
dblink_res_error(PGconn *conn, const char *conname, PGresult *res,
const char *dblink_context_msg, bool fail)
{
int level;
char *pg_diag_sqlstate = PQresultErrorField(res, PG_DIAG_SQLSTATE);
@ -2702,6 +2707,14 @@ dblink_res_error(const char *conname, PGresult *res, const char *dblink_context_
xpstrdup(message_hint, pg_diag_message_hint);
xpstrdup(message_context, pg_diag_context);
/*
* 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.
*/
if (message_primary == NULL)
message_primary = PQerrorMessage(conn);
if (res)
PQclear(res);