On 12/21/2016 04:22 PM, Tom Lane wrote: > Joe Conway <m...@joeconway.com> writes: >> I did notice that postgres_fdw has the following stanza that I don't see >> in dblink: > >> 8<------------------ >> /* >> * 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); >> 8<------------------ > >> I wonder if the original issue on pgsql-bugs was a connection-level >> failure rather than OOM? Seems like dblink ought to do the same. > > Oooh ... I had thought that code was in both, which was why I was having > a hard time explaining the OP's failure. But I see you're right, > which provides a very straightforward explanation for the report. > I believe that if libpq is unable to malloc a PGresult, it will return > NULL but put an "out of memory" message into the PGconn's error buffer. > I had supposed that we'd capture and report the latter, but as the > dblink code stands, it won't. > > In short, yes, please copy that bit into dblink.
The attached should do the trick I think. You think it is reasonable to backpatch this part too? Joe -- Crunchy Data - http://crunchydata.com PostgreSQL Support for Secure Enterprises Consulting, Training, & Open Source Development
diff --git a/contrib/dblink/dblink.c b/contrib/dblink/dblink.c
index ee45cd2..db3085a 100644
*** a/contrib/dblink/dblink.c
--- b/contrib/dblink/dblink.c
*************** static Relation get_rel_from_relname(tex
*** 112,118 ****
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 char *get_connect_string(const char *servername);
static char *escape_param_str(const char *from);
static void validate_pkattnums(Relation rel,
--- 112,119 ----
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(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,
*************** dblink_open(PG_FUNCTION_ARGS)
*** 427,433 ****
res = PQexec(conn, buf.data);
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
! dblink_res_error(conname, res, "could not open cursor", fail);
PG_RETURN_TEXT_P(cstring_to_text("ERROR"));
}
--- 428,434 ----
res = PQexec(conn, buf.data);
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
! dblink_res_error(conn, conname, res, "could not open cursor", fail);
PG_RETURN_TEXT_P(cstring_to_text("ERROR"));
}
*************** dblink_close(PG_FUNCTION_ARGS)
*** 496,502 ****
res = PQexec(conn, buf.data);
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
! dblink_res_error(conname, res, "could not close cursor", fail);
PG_RETURN_TEXT_P(cstring_to_text("ERROR"));
}
--- 497,503 ----
res = PQexec(conn, buf.data);
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
! dblink_res_error(conn, conname, res, "could not close cursor", fail);
PG_RETURN_TEXT_P(cstring_to_text("ERROR"));
}
*************** dblink_fetch(PG_FUNCTION_ARGS)
*** 599,605 ****
(PQresultStatus(res) != PGRES_COMMAND_OK &&
PQresultStatus(res) != PGRES_TUPLES_OK))
{
! dblink_res_error(conname, res, "could not fetch from cursor", fail);
return (Datum) 0;
}
else if (PQresultStatus(res) == PGRES_COMMAND_OK)
--- 600,607 ----
(PQresultStatus(res) != PGRES_COMMAND_OK &&
PQresultStatus(res) != PGRES_TUPLES_OK))
{
! dblink_res_error(conn, conname, res,
! "could not fetch from cursor", fail);
return (Datum) 0;
}
else if (PQresultStatus(res) == PGRES_COMMAND_OK)
*************** dblink_record_internal(FunctionCallInfo
*** 750,757 ****
if (PQresultStatus(res) != PGRES_COMMAND_OK &&
PQresultStatus(res) != PGRES_TUPLES_OK)
{
! dblink_res_error(conname, res, "could not execute query",
! fail);
/* if fail isn't set, we'll return an empty query result */
}
else
--- 752,759 ----
if (PQresultStatus(res) != PGRES_COMMAND_OK &&
PQresultStatus(res) != PGRES_TUPLES_OK)
{
! dblink_res_error(conn, conname, res,
! "could not execute query", fail);
/* if fail isn't set, we'll return an empty query result */
}
else
*************** materializeQueryResult(FunctionCallInfo
*** 996,1002 ****
PGresult *res1 = res;
res = NULL;
! dblink_res_error(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)
--- 998,1005 ----
PGresult *res1 = res;
res = NULL;
! 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)
*************** dblink_exec(PG_FUNCTION_ARGS)
*** 1431,1437 ****
(PQresultStatus(res) != PGRES_COMMAND_OK &&
PQresultStatus(res) != PGRES_TUPLES_OK))
{
! dblink_res_error(conname, res, "could not execute command", fail);
/*
* and save a copy of the command status string to return as our
--- 1434,1441 ----
(PQresultStatus(res) != PGRES_COMMAND_OK &&
PQresultStatus(res) != PGRES_TUPLES_OK))
{
! dblink_res_error(conn, conname, res,
! "could not execute command", fail);
/*
* and save a copy of the command status string to return as our
*************** dblink_connstr_check(const char *connstr
*** 2662,2668 ****
}
static void
! dblink_res_error(const char *conname, PGresult *res, const char *dblink_context_msg, bool fail)
{
int level;
char *pg_diag_sqlstate = PQresultErrorField(res, PG_DIAG_SQLSTATE);
--- 2666,2673 ----
}
static void
! 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);
*************** dblink_res_error(const char *conname, PG
*** 2696,2701 ****
--- 2701,2714 ----
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);
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