cat recovery

The recovery command is a view of index shard recoveries, both on-going and previously completed. It is a more compact view of the JSON recovery API.

A recovery event occurs anytime an index shard moves to a different node in the cluster. This can happen during a snapshot recovery, a change in replication level, node failure, or on node startup. This last type is called a local gateway recovery and is the normal way for shards to be loaded from disk when a node starts up.

As an example, here is what the recovery state of a cluster may look like when there are no shards in transit from one node to another:

> curl -XGET 'localhost:9200/_cat/recovery?v'
index shard time type    stage source target files percent bytes     percent
wiki  0     73   gateway done  hostA  hostA  36    100.0%  24982806 100.0%
wiki  1     245  gateway done  hostA  hostA  33    100.0%  24501912 100.0%
wiki  2     230  gateway done  hostA  hostA  36    100.0%  30267222 100.0%

In the above case, the source and target nodes are the same because the recovery type was gateway, i.e. they were read from local storage on node start.

Now let’s see what a live recovery looks like. By increasing the replica count of our index and bringing another node online to host the replicas, we can see what a live shard recovery looks like.

> curl -XPUT 'localhost:9200/wiki/_settings' -d'{"number_of_replicas":1}'
{"acknowledged":true}

> curl -XGET 'localhost:9200/_cat/recovery?v'
index shard time type    stage source target files percent bytes    percent
wiki  0     1252 gateway done  hostA  hostA  4     100.0%  23638870 100.0%
wiki  0     1672 replica index hostA  hostB  4     75.0%   23638870 48.8%
wiki  1     1698 replica index hostA  hostB  4     75.0%   23348540 49.4%
wiki  1     4812 gateway done  hostA  hostA  33    100.0%  24501912 100.0%
wiki  2     1689 replica index hostA  hostB  4     75.0%   28681851 40.2%
wiki  2     5317 gateway done  hostA  hostA  36    100.0%  30267222 100.0%

We can see in the above listing that our 3 initial shards are in various stages of being replicated from one node to another. Notice that the recovery type is shown as replica. The files and bytes copied are real-time measurements.

Finally, let’s see what a snapshot recovery looks like. Assuming I have previously made a backup of my index, I can restore it using the snapshot and restore API.

> curl -XPOST 'localhost:9200/_snapshot/imdb/snapshot_2/_restore'
{"acknowledged":true}
> curl -XGET 'localhost:9200/_cat/recovery?v'
index shard time type     stage repository snapshot files percent bytes percent
imdb  0     1978 snapshot done  imdb       snap_1   79    8.0%    12086 9.0%
imdb  1     2790 snapshot index imdb       snap_1   88    7.7%    11025 8.1%
imdb  2     2790 snapshot index imdb       snap_1   85    0.0%    12072 0.0%
imdb  3     2796 snapshot index imdb       snap_1   85    2.4%    12048 7.2%
imdb  4     819  snapshot init  imdb       snap_1   0     0.0%    0     0.0%