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Don't expire keys when loading an RDB after a SYNC

The cron is responsible for expiring keys. When keys are expired at
load time, it is possible that the snapshot of a master node gets
modified. This can in turn lead to inconsistencies in the data set.

A more concrete example of this behavior follows. A user reported a
slave that would show an monotonically increase input buffer length,
shortly after completing a SYNC. Also, `INFO` output showed a single
blocked client, which could only be the master link. Investigation
showed that indeed the `BRPOP` command was fed by the master. This
command can only end up in the stream of write operations when it did
NOT block, and effectively executed `RPOP`. However, when the key
involved in the `BRPOP` is expired BEFORE the command is executed, the
client executing it will block. The client in this case, is the master
link.
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1 parent 8b8261e commit aa794ac06d196945941b6a226bf40d36d16cf9cf @pietern pietern committed Jan 14, 2012
Showing with 6 additions and 2 deletions.
  1. +6 −2 src/rdb.c
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@@ -993,8 +993,12 @@ int rdbLoad(char *filename) {
if ((key = rdbLoadStringObject(fp)) == NULL) goto eoferr;
/* Read value */
if ((val = rdbLoadObject(type,fp)) == NULL) goto eoferr;
- /* Check if the key already expired */
- if (expiretime != -1 && expiretime < now) {
+ /* Check if the key already expired. This function is used when loading
+ * an RDB file from disk, either at startup, or when an RDB was
+ * received from the master. In the latter case, the master is
+ * responsible for key expiry. If we would expire keys here, the
+ * snapshot taken by the master may not be reflected on the slave. */
+ if (server.masterhost == NULL && expiretime != -1 && expiretime < now) {
decrRefCount(key);
decrRefCount(val);
continue;

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