Adding upstream version 1.9.1.upstream/1.9.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 25 insertions, 0 deletions

diff --git a/iredis/data/commands/cluster-set-config-epoch.md b/iredis/data/commands/cluster-set-config-epoch.md
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+This command sets a specific _config epoch_ in a fresh node. It only works when:
+
+1. The nodes table of the node is empty.
+2. The node current _config epoch_ is zero.
+
+These prerequisites are needed since usually, manually altering the
+configuration epoch of a node is unsafe, we want to be sure that the node with
+the higher configuration epoch value (that is the last that failed over) wins
+over other nodes in claiming the hash slots ownership.
+
+However there is an exception to this rule, and it is when a new cluster is
+created from scratch. Redis Cluster _config epoch collision resolution_
+algorithm can deal with new nodes all configured with the same configuration at
+startup, but this process is slow and should be the exception, only to make sure
+that whatever happens, two more nodes eventually always move away from the state
+of having the same configuration epoch.
+
+So, using `CONFIG SET-CONFIG-EPOCH`, when a new cluster is created, we can
+assign a different progressive configuration epoch to each node before joining
+the cluster together.
+
+@return
+
+@simple-string-reply: `OK` if the command was executed successfully, otherwise
+an error is returned.