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Fix handling of errors in libpq pipelines

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The logic to keep the libpq command queue in sync with queries that have
been processed had a bug when errors were returned for reasons other
than problems in queries -- for example, when a connection is lost.  We
incorrectly consumed an element from the command queue every time, but
this is wrong and can lead to the queue becoming empty ahead of time,
leading to later malfunction: PQgetResult would return nothing,
potentially causing the calling application to enter a busy loop.

Fix by making the SYNC queue element a barrier that can only be consumed
when a SYNC message is received.

Backpatch to 14.

Reported by: Иван Трофимов (Ivan Trofimov) <i.trofimow@yandex.ru>
Discussion: https://postgr.es/m/17948-fcace7557e449957@postgresql.org
This commit is contained in:
Alvaro Herrera
2023-12-05 12:43:24 +01:00
parent 63c5df126a
commit b8ba7344e9
3 changed files with 40 additions and 25 deletions
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3
src/interfaces/libpq/libpq-int.h
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@@ -698,7 +698,8 @@ extern void pqSaveMessageField(PGresult *res, char code,
extern void pqSaveParameterStatus(PGconn *conn, const char *name,
const char *value);
extern int pqRowProcessor(PGconn *conn, const char **errmsgp);
extern void pqCommandQueueAdvance(PGconn *conn);
extern void pqCommandQueueAdvance(PGconn *conn, bool isReadyForQuery,
bool gotSync);
extern int PQsendQueryContinue(PGconn *conn, const char *query);
/* === in fe-protocol3.c === */