278 lines
8.0 KiB
Plaintext
278 lines
8.0 KiB
Plaintext
[[indices-synced-flush-api]]
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=== Synced flush API
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++++
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<titleabbrev>Synced flush</titleabbrev>
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++++
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Performs a synced flush on one or more indices.
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[source,console]
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--------------------------------------------------
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POST /twitter/_flush/synced
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--------------------------------------------------
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// TEST[skip: Synced flush can conflict with scheduled flushes in doc tests]
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[[synced-flush-api-request]]
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==== {api-request-title}
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`POST /<index>/flush/synced`
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`GET /<index>/flush/synced`
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`POST /flush/synced`
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`GET /flush/synced`
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[[synced-flush-api-desc]]
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==== {api-description-title}
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[[synced-flush-using-api]]
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===== Use the synced flush API
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Use the synced flush API to manually initiate a synced flush.
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This can be useful for a planned cluster restart where
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you can stop indexing but don't want to wait for 5 minutes until all indices
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are marked as inactive and automatically sync-flushed.
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You can request a synced flush even if there is ongoing indexing activity, and
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{es} will perform the synced flush on a "best-effort" basis: shards that do not
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have any ongoing indexing activity will be successfully sync-flushed, and other
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shards will fail to sync-flush. The successfully sync-flushed shards will have
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faster recovery times as long as the `sync_id` marker is not removed by a
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subsequent flush.
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[[synced-flush-overview]]
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===== Synced flush overview
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{es} keeps track of which shards have received indexing activity recently, and
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considers shards that have not received any indexing operations for 5 minutes to
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be inactive.
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When a shard becomes inactive {es} performs a special kind of flush
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known as a *synced flush*. A synced flush performs a normal
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<<indices-flush,flush>> on each replica of the shard, and then adds a marker known
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as the `sync_id` to each replica to indicate that these copies have identical
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Lucene indices. Comparing the `sync_id` markers of the two copies is a very
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efficient way to check whether they have identical contents.
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When allocating shard replicas, {es} must ensure that each replica contains the
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same data as the primary. If the shard copies have been synced-flushed and the
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replica shares a `sync_id` with the primary then {es} knows that the two copies
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have identical contents. This means there is no need to copy any segment files
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from the primary to the replica, which saves a good deal of time during
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recoveries and restarts.
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This is particularly useful for clusters having lots of indices which are very
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rarely updated, such as with time-based indices. Without the synced flush
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marker, recovery of this kind of cluster would be much slower.
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[[synced-flush-sync-id-markers]]
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===== Check for `sync_id` markers
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To check whether a shard has a `sync_id` marker or not, look for the `commit`
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section of the shard stats returned by the <<indices-stats,indices stats>> API:
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[source,console]
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--------------------------------------------------
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GET /twitter/_stats?filter_path=**.commit&level=shards <1>
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--------------------------------------------------
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// TEST[skip: Synced flush can conflict with scheduled flushes in doc tests]
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<1> `filter_path` is used to reduce the verbosity of the response, but is entirely optional
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The API returns the following response:
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[source,console-result]
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--------------------------------------------------
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{
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"indices": {
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"twitter": {
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"shards": {
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"0": [
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{
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"commit" : {
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"id" : "3M3zkw2GHMo2Y4h4/KFKCg==",
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"generation" : 3,
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"user_data" : {
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"translog_uuid" : "hnOG3xFcTDeoI_kvvvOdNA",
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"history_uuid" : "XP7KDJGiS1a2fHYiFL5TXQ",
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"local_checkpoint" : "-1",
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"translog_generation" : "2",
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"max_seq_no" : "-1",
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"sync_id" : "AVvFY-071siAOuFGEO9P", <1>
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"max_unsafe_auto_id_timestamp" : "-1",
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"min_retained_seq_no" : "0"
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},
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"num_docs" : 0
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}
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}
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]
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}
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}
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}
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}
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--------------------------------------------------
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// TEST[skip: Synced flush can conflict with scheduled flushes in doc tests]
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<1> the `sync id` marker
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NOTE: The `sync_id` marker is removed as soon as the shard is flushed again, and
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{es} may trigger an automatic flush of a shard at any time if there are
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unflushed operations in the shard's translog. In practice this means that one
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should consider any indexing operation on an index as having removed its
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`sync_id` markers.
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[[synced-flush-api-path-params]]
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==== {api-path-parms-title}
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include::{docdir}/rest-api/common-parms.asciidoc[tag=index]
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+
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To sync-flush all indices,
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omit this parameter
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or use a value of `_all` or `*`.
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[[synced-flush-api-query-params]]
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==== {api-query-parms-title}
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include::{docdir}/rest-api/common-parms.asciidoc[tag=allow-no-indices]
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include::{docdir}/rest-api/common-parms.asciidoc[tag=expand-wildcards]
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+
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Defaults to `open`.
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include::{docdir}/rest-api/common-parms.asciidoc[tag=index-ignore-unavailable]
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[[synced-flush-api-response-codes]]
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==== {api-response-codes-title}
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`200`::
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All shards successfully sync-flushed.
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`409`::
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A replica shard failed to sync-flush.
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[[synced-flush-api-example]]
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==== {api-examples-title}
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[[synced-flush-api-specific-ex]]
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===== Sync-flush a specific index
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[source,console]
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----
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POST /kimchy/_flush/synced
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----
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// TEST[skip: Synced flush can conflict with scheduled flushes in doc tests]
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[[synced-flush-api-multi-ex]]
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===== Synch-flush several indices
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[source,console]
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--------------------------------------------------
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POST /kimchy,elasticsearch/_flush/synced
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--------------------------------------------------
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// TEST[skip: Synced flush can conflict with scheduled flushes in doc tests]
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[[synced-flush-api-all-ex]]
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===== Sync-flush all indices
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[source,console]
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--------------------------------------------------
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POST /_flush/synced
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--------------------------------------------------
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// TEST[skip: Synced flush can conflict with scheduled flushes in doc tests]
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The response contains details about how many shards were successfully
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sync-flushed and information about any failure.
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The following response indicates two shards
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and one replica shard
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successfully sync-flushed:
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[source,console-result]
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--------------------------------------------------
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{
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"_shards": {
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"total": 2,
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"successful": 2,
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"failed": 0
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},
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"twitter": {
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"total": 2,
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"successful": 2,
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"failed": 0
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}
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}
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--------------------------------------------------
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// TEST[skip: Synced flush can conflict with scheduled flushes in doc tests]
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The following response indicates one shard group failed
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due to pending operations:
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[source,console-result]
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--------------------------------------------------
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{
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"_shards": {
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"total": 4,
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"successful": 2,
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"failed": 2
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},
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"twitter": {
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"total": 4,
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"successful": 2,
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"failed": 2,
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"failures": [
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{
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"shard": 1,
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"reason": "[2] ongoing operations on primary"
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}
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]
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}
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}
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--------------------------------------------------
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// TEST[skip: Synced flush can conflict with scheduled flushes in doc tests]
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Sometimes the failures are specific to a shard replica. The copies that failed
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will not be eligible for fast recovery but those that succeeded still will be.
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This case is reported as follows:
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[source,console-result]
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--------------------------------------------------
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{
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"_shards": {
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"total": 4,
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"successful": 1,
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"failed": 1
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},
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"twitter": {
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"total": 4,
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"successful": 3,
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"failed": 1,
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"failures": [
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{
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"shard": 1,
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"reason": "unexpected error",
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"routing": {
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"state": "STARTED",
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"primary": false,
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"node": "SZNr2J_ORxKTLUCydGX4zA",
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"relocating_node": null,
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"shard": 1,
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"index": "twitter"
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}
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}
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]
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}
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}
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--------------------------------------------------
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// TEST[skip: Synced flush can conflict with scheduled flushes in doc tests]
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