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Fix replicas migration by adding a new flag.

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Some time ago I broken replicas migration (reported in #2924).
The idea was to prevent masters without replicas from getting replicas
because of replica migration, I remember it to create issues with tests,
but there is no clue in the commit message about why it was so
undesirable.

However my patch as a side effect totally ruined the concept of replicas
migration since we want it to work also for instances that, technically,
never had slaves in the past: promoted slaves.

So now instead the ability to be targeted by replicas migration, is a
new flag "migrate-to". It only applies to masters, and is set in the
following two cases:

1. When a master gets a slave, it is set.
2. When a slave turns into a master because of fail over, it is set.

This way replicas migration targets are only masters that used to have
slaves, and slaves of masters (that used to have slaves... obviously)
and are promoted.

The new flag is only internal, and is never exposed in the output nor
persisted in the nodes configuration, since all the information to
handle it are implicit in the cluster configuration we already have.
This commit is contained in:
antirez
2015-12-09 22:52:53 +01:00
parent f1472252eb
commit e0f22df995
2 changed files with 31 additions and 20 deletions
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2
src/cluster.h
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@ -53,7 +53,7 @@ typedef struct clusterLink {
#define CLUSTER_NODE_HANDSHAKE 32 /* We have still to exchange the first ping */
#define CLUSTER_NODE_NOADDR 64 /* We don't know the address of this node */
#define CLUSTER_NODE_MEET 128 /* Send a MEET message to this node */
#define CLUSTER_NODE_PROMOTED 256 /* Master was a slave promoted by failover */
#define CLUSTER_NODE_MIGRATE_TO 256 /* Master elegible for replica migration. */
#define CLUSTER_NODE_NULL_NAME "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"
#define nodeIsMaster(n) ((n)->flags & CLUSTER_NODE_MASTER)