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commit    6c75fb6b3dbeda4dac19cee8f2d5cc7f38f362ee
Author:   Fujii Masao <fujii@postgresql.org>
Date:     Fri Dec 16 17:20:59 2016 +0000

    Ensure that num_sync is greater than zero in synchronous_standby_names.
    
    Previously num_sync could be set to zero and this setting caused
    an assertion failure. This means that multiple synchronous standbys
    code should assume that num_sync is greater than zero.
    Also setting num_sync to zero is nonsense because it's basically
    the configuration for synchronous replication. If users want not to
    make transaction commits wait for any standbys,
    synchronous_standby_names should be emptied to disable synchronous
    replication instead of setting num_sync to zero.
    
    This patch forbids users from setting num_sync to zero in
    synchronous_standby_names. If zero is specified, an error will
    happen during processing the parameter settings.
    
    Back-patch to 9.6 where multiple synchronous standbys feature was added.
    
    Patch by me. Reviewed by Tom Lane.
    Discussion: <CAHGQGwHWB3izc6cXuFLh5kOcAbFXaRhhgwd-X5PeN9TEjxqXwg@mail.gmail.com>


 src/backend/replication/syncrep.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/backend/replication/syncrep.c b/src/backend/replication/syncrep.c
index b442d061ec0..3dfff04405d 100644
--- a/src/backend/replication/syncrep.c
+++ b/src/backend/replication/syncrep.c
@@ -922,6 +922,13 @@ check_synchronous_standby_names(char **newval, void **extra, GucSource source)
 			return false;
 		}
 
+		if (syncrep_parse_result->num_sync <= 0)
+		{
+			GUC_check_errmsg("number of synchronous standbys (%d) must be greater than zero",
+							 syncrep_parse_result->num_sync);
+			return false;
+		}
+
 		/* GUC extra value must be malloc'd, not palloc'd */
 		pconf = (SyncRepConfigData *)
 			malloc(syncrep_parse_result->config_size);


[parent: 6f734554c388]