Shrink
editShrink
editPhases allowed: hot, warm.
Sets a source index to read-only and shrinks it into
a new index with fewer primary shards. The name of the resulting index is
shrink-<random-uuid>-<original-index-name>
. This action corresponds to the
shrink API.
After the shrink
action, any aliases that pointed to the source index point to
the new shrunken index. If ILM performs the shrink
action on a backing
index for a data stream, the shrunken index replaces the source index in the
stream. You cannot perform the shrink
action on a write index.
To use the shrink
action in the hot
phase, the rollover
action must be
present. If no rollover action is configured, ILM will reject the policy.
The shrink action will unset the index’s index.routing.allocation.total_shards_per_node
setting, meaning that there will be no limit. This is to ensure that all shards of the
index can be copied to a single node. This setting change will persist on the index
even after the step completes.
If the shrink action is used on a follower index, policy execution waits until the leader index rolls over (or is otherwise marked complete), then converts the follower index into a regular index with the unfollow action before performing the shrink operation.
Shrink options
edit-
number_of_shards
-
(Optional, integer)
Number of shards to shrink to.
Must be a factor of the number of shards in the source index. This parameter conflicts with
max_primary_shard_size
, only one of them may be set. -
max_primary_shard_size
-
(Optional, byte units)
The max primary shard size for the target index. Used to find the optimum number of shards for the target index.
When this parameter is set, each shard’s storage in the target index will not be greater than the parameter.
The shards count of the target index will still be a factor of the source index’s shards count, but if the parameter
is less than the single shard size in the source index, the shards count for the target index will be equal to the source index’s shards count.
For example, when this parameter is set to 50gb, if the source index has 60 primary shards with totaling 100gb, then the
target index will have 2 primary shards, with each shard size of 50gb; if the source index has 60 primary shards
with totaling 1000gb, then the target index will have 20 primary shards; if the source index has 60 primary shards
with totaling 4000gb, then the target index will still have 60 primary shards. This parameter conflicts
with
number_of_shards
in thesettings
, only one of them may be set.
Example
editSet the number of shards of the new shrunken index explicitly
editresponse = client.ilm.put_lifecycle( policy: 'my_policy', body: { policy: { phases: { warm: { actions: { shrink: { number_of_shards: 1 } } } } } } ) puts response
PUT _ilm/policy/my_policy { "policy": { "phases": { "warm": { "actions": { "shrink" : { "number_of_shards": 1 } } } } } }
Calculate the optimal number of primary shards for a shrunken index
editThe following policy uses the max_primary_shard_size
parameter to
automatically calculate the new shrunken index’s primary shard count based on
the source index’s storage size.
response = client.ilm.put_lifecycle( policy: 'my_policy', body: { policy: { phases: { warm: { actions: { shrink: { max_primary_shard_size: '50gb' } } } } } } ) puts response
PUT _ilm/policy/my_policy { "policy": { "phases": { "warm": { "actions": { "shrink" : { "max_primary_shard_size": "50gb" } } } } } }
Shard allocation for shrink
editDuring a shrink
action, ILM allocates the source index’s primary shards
to one node. After shrinking the index, ILM reallocates the shrunken
index’s shards to the appropriate nodes based on your allocation rules.
These allocation steps can fail for several reasons, including:
-
A node is removed during the
shrink
action. - No node has enough disk space to host the source index’s shards.
- Elasticsearch cannot reallocate the shrunken index due to conflicting allocation rules.
When one of the allocation steps fails, ILM waits for the period set in
index.lifecycle.step.wait_time_threshold
,
which defaults to 12 hours. This threshold period lets the cluster resolve any
issues causing the allocation failure.
If the threshold period passes and ILM has not yet shrunk the index,
ILM attempts to allocate the source index’s primary shards to another
node. If ILM shrunk the index but could not reallocate the shrunken
index’s shards during the threshold period, ILM deletes the shrunken
index and re-attempts the entire shrink
action.