cat shards
editcat shards
editThe shards
command is the detailed view of what nodes contain which
shards. It will tell you if it’s a primary or replica, the number of
docs, the bytes it takes on disk, and the node where it’s located.
Here we see a single index, with one primary shard and no replicas:
GET _cat/shards
This will return
twitter 0 p STARTED 3014 31.1mb 192.168.56.10 H5dfFeA twitter 0 r UNASSIGNED
Index pattern
editIf you have many shards, you may wish to limit which indices show up
in the output. You can always do this with grep
, but you can save
some bandwidth by supplying an index pattern to the end.
GET _cat/shards/twitt*
Which will return the following
twitter 0 p STARTED 3014 31.1mb 192.168.56.10 H5dfFeA twitter 0 r UNASSIGNED
Relocation
editLet’s say you’ve checked your health and you see a relocating shards. Where are they from and where are they going?
GET _cat/shards
A relocating shard will be shown as follows
twitter 0 p RELOCATING 3014 31.1mb 192.168.56.10 H5dfFeA -> -> 192.168.56.30 bGG90GE
Shard states
editBefore a shard can be used, it goes through an INITIALIZING
state.
shards
can show you which ones.
GET _cat/shards
You can the the initializing state in the response like this
twitter 0 p STARTED 3014 31.1mb 192.168.56.10 H5dfFeA twitter 0 r INITIALIZING 0 14.3mb 192.168.56.30 bGG90GE
If a shard cannot be assigned, for example you’ve overallocated the
number of replicas for the number of nodes in the cluster, the shard
will remain UNASSIGNED
with the reason code ALLOCATION_FAILED
.
You can use the shards API to find out that reason.
GET _cat/shards?h=index,shard,prirep,state,unassigned.reason
The reason for an unassigned shard will be listed as the last field
twitter 0 p STARTED 3014 31.1mb 192.168.56.10 H5dfFeA twitter 0 r STARTED 3014 31.1mb 192.168.56.30 bGG90GE twitter 0 r STARTED 3014 31.1mb 192.168.56.20 I8hydUG twitter 0 r UNASSIGNED ALLOCATION_FAILED
Reasons for unassigned shard
editThese are the possible reasons for a shard to be in a unassigned state:
|
Unassigned as a result of an API creation of an index. |
|
Unassigned as a result of a full cluster recovery. |
|
Unassigned as a result of opening a closed index. |
|
Unassigned as a result of importing a dangling index. |
|
Unassigned as a result of restoring into a new index. |
|
Unassigned as a result of restoring into a closed index. |
|
Unassigned as a result of explicit addition of a replica. |
|
Unassigned as a result of a failed allocation of the shard. |
|
Unassigned as a result of the node hosting it leaving the cluster. |
|
Unassigned as a result of explicit cancel reroute command. |
|
When a shard moves from started back to initializing, for example, with shadow replicas. |
|
A better replica location is identified and causes the existing replica allocation to be cancelled. |