Commit Graph

4105 Commits

Author SHA1 Message Date
Ryan Ernst fbfc5a327c Fix checkstyle and test for logging output stream
Commit a156629b didn't quite fix the botched backport. This commit does.
2020-01-25 14:13:47 -08:00
Ryan Ernst a156629b4a Fix backport compilation
Java 8 doesn't have a PrintStream ctor which takes a Charset object,
only a charset name. This fixes that.
2020-01-25 11:13:33 -08:00
Ryan Ernst a564cac7ba Capture stdout and stderr to log4j log (#50259)
This commit overrides the stdout and stderr print streams to be
redirected to the main elasticsearch.log file. While the Elasticsearch
project ensures stdout and stderr are not written to, the jdk or 3rd
party libs may do this, which can be unexepected for users used to
looking the elasticsearch log.

closes #50156
2020-01-25 11:00:01 -08:00
Armin Braun ef94a5863a
Fix RareClusterStateIT Cancelling Publication too Early (#51429) (#51434)
Wait for the cluster to have settled down and have the same accepted version on all nodes before
executing and cancelling request so that a slow CS accept on one node doesn't make it fall behind
and then get sent the full CS because of the diff-version mismatch, breaking the mechanics of this test.

Closes #51308
2020-01-24 20:33:45 +01:00
Armin Braun af1ff52e70
Fix TransportMasterNodeAction not Retrying NodeClosedException (#51325) (#51437)
Added node closed exception to the retryable remote exceptions as it's possible to run into this exception instead of a connect exception when the master node is just shutting down but still responding to requests.
2020-01-24 20:33:13 +01:00
Armin Braun f0d8c785e3
Fix Inconsistent Shard Failure Count in Failed Snapshots (#51416) (#51426)
* Fix Inconsistent Shard Failure Count in Failed Snapshots

This fix was necessary to allow for the below test enhancement:
We were not adding shard failure entries to a failed snapshot for those
snapshot entries that were never attempted because the snapshot failed during
the init stage and wasn't partial. This caused the never attempted snapshots
to be counted towards the successful shard count which seems wrong and
broke repository consistency tests.

Also, this change adjusts snapshot resiliency tests to run another snapshot
at the end of each test run to guarantee a correct `index.latest` blob exists
after each run.

Closes #47550
2020-01-24 18:20:47 +01:00
Ryan Ernst 144e037941 Ignore order of indices in hidden indices test (#51383)
The order indices are returned in in the metadata is not guaranteed.
This commit accounts for any possible ordering in assertions about
hidden indices.

closes #51340
2020-01-23 15:49:32 -08:00
Nhat Nguyen 1ca5dd13de
Flush instead of synced-flush inactive shards (#51365)
If all nodes are on 7.6, we prefer to perform a normal flush 
instead of synced flush when a shard becomes inactive.

Backport of #49126
2020-01-23 17:20:57 -05:00
David Turner 0152c40724
Log when probe succeeds but full connection fails (#51304) (#51357)
It is permitted for nodes to accept transport connections at addresses other
than their publish address, which allows a good deal of flexibility when
configuring discovery. However, it is not unusual for users to misconfigure
nodes to pick a publish address which is inaccessible to other nodes. We see
this happen a lot if the nodes are on different networks separated by a proxy,
or if the nodes are running in Docker with the wrong kind of network config.

In this case we offer no useful feedback to the user unless they enable
TRACE-level logs. It's particularly tricky to diagnose because if we test
connectivity between the nodes (using their discovery addresses) then all will
appear well.

This commit adds a WARN-level log if this kind of misconfiguration is detected:
the probe connection has succeeded (to indicate that we are really talking to a
healthy Elasticsearch node) but the followup connection attempt fails.

It also tidies up some loose ends in `HandshakingTransportAddressConnector`,
removing some TODOs that need not be completed, and registering its
accidentally-unregistered timeout settings.
2020-01-23 17:27:59 +00:00
Nhat Nguyen acf84b68cb Do not wrap soft-deletes reader for segment stats (#51331)
IndexWriter might not filter out fully deleted segments if retention
leases exist or the number of the retaining operations is non-zero.
SoftDeletesDirectoryReaderWrapper, however, always filters out fully
deleted segments.

This change uses the original directory reader when calculating segment
stats instead.

Relates #51192
Closes #51303
2020-01-23 08:43:06 -05:00
Armin Braun 4e8ab43a3e
Simplify Snapshot Initialization (#51256) (#51344)
We were loading `RepositoryData` twice during snapshot initialization,
redundantly checking if a snapshot existed already.
The first snapshot existence check is somewhat redundant because a snapshot could be
created between loading `RepositoryData` and updating the cluster state with the `INIT`
state snapshot entry.
Also, it is much safer to do the subsequent checks for index existence in the repo and
and the presence of old version snapshots once the `INIT` state entry prevents further
snapshots from being created concurrently.
While the current state of things will never lead to corruption on a concurrent snapshot
creation, it could result in a situation (though unlikely) where all the snapshot's work
is done on the data nodes, only to find out that the repository generation was off during
snapshot finalization, failing there and leaving a bunch of dead data in the repository
that won't be used in a subsequent snapshot (because the shard generation was never referenced
due to the failed snapshot finalization).

Note: This is a step on the way to parallel repository operations by making snapshot related CS
and repo related CS more tightly correlated.
2020-01-23 14:29:35 +01:00
Henning Andersen 8c8d0dbacc Revert "Workaround for JDK 14 EA FileChannel.map issue (#50523)" (#51323)
This reverts commit c7fd24ca1569a809b499caf34077599e463bb8d6.

Now that JDK-8236582 is fixed in JDK 14 EA, we can revert the workaround.

Relates #50523 and #50512
2020-01-23 11:27:02 +01:00
Nhat Nguyen 157b352b47 Exclude nested documents in LuceneChangesSnapshot (#51279)
LuceneChangesSnapshot can be slow if nested documents are heavily used.
Also, it estimates the number of operations to be recovered in peer
recoveries inaccurately. With this change, we prefer excluding the
nested non-root documents in a Lucene query instead.
2020-01-22 17:33:28 -05:00
Nirmal Chidambaram f193e527a1 Short circuited to MatchNone for non-participating slice (#51207)
In case of numSlices = numShards, use a MatchNone query
instead of boolean with a MatchNone - MUST clause

Backport for #51207
2020-01-22 17:04:53 -05:00
Igor Motov 08e9c673e5 Fix leftover mentions of method parameter in Percentile Aggs (#51272)
The method parameter is not used in the percentile aggs, instead
the method is determined by the presence of `hdr` or `tdigest`
objects.

Relates to #8324
2020-01-22 10:03:35 -05:00
Andrei Dan 123266714b
ILM wait for active shards on rolled index in a separate step (#50718) (#51296)
After we rollover the index we wait for the configured number of shards for the
rolled index to become active (based on the index.write.wait_for_active_shards
setting which might be present in a template, or otherwise in the default case,
for the primaries to become active).
This wait might be long due to disk watermarks being tripped, replicas not
being able to spring to life due to cluster nodes reconfiguration and others
and, the RolloverStep might not complete successfully due to this inherent
transient situation, albeit the rolled index having been created.

(cherry picked from commit 457a92fb4c68c55976cc3c3e2f00a053dd2eac70)
Signed-off-by: Andrei Dan <andrei.dan@elastic.co>
2020-01-22 11:01:52 +00:00
Armin Braun 7b4c2bfdc4
Fix Overly Optimistic Request Deduplication (#51270) (#51291)
On master failover we have to resent all the shard failed messages,
but the transport requests remain the same in the eyes of `equals`.
If the master failover is registered and the requests to the new master
are sent before all the callbacks have executed and the request to the
old master removed from the deduplicator then the requuests to the new
master will incorrectly fail and the snapshot get stuck.

Closes #51253
2020-01-22 11:38:40 +01:00
Stuart Tettemer 41c15b438d
Scripting: Add char position of script errors (#51069) (#51266)
Add the character position of a scripting error to error responses.

The contents of the `position` field are experimental and subject to
change.  Currently, `offset` refers to the character location where the
error was encountered, `start` and `end` define a range of characters
that contain the error.

eg.
```
{
  "error": {
    "root_cause": [
      {
        "type": "script_exception",
        "reason": "runtime error",
        "script_stack": [
          "y = x;",
          "     ^---- HERE"
        ],
        "script": "def x = new ArrayList(); Map y = x;",
        "lang": "painless",
        "position": {
          "offset": 33,
          "start": 29,
          "end": 35
        }
      }
```

Refs: #50993
2020-01-21 13:45:59 -07:00
Nik Everett ca15a3f5a8
Add "did you mean" to unknown queries (#51177) (#51254)
This replaces the message we return for unknown queries with the standard
one that we use for unknown fields from `ObjectParser`. This is nice
because it includes "did you mean". One day we might convert parsing
queries to using object parser, but that looks complex. This change is
much smaller and seems useful.
2020-01-21 12:45:52 -05:00
Paul Sanwald d186e470ff version bump for 7.5.3 2020-01-21 10:59:55 -05:00
Nik Everett 788836ea3f
Revert "Begin moving date_histogram to offset rounding (backport of #50873) (#50978)" (#51239)
This reverts commit 9a3d4db840. It was
subtly broken in ways we didn't have tests for.
2020-01-21 08:50:02 -05:00
Przemyslaw Gomulka 0513d8dca3
Add SPI jvm option to SystemJvmOptions (#50916)
Adding back accidentally removed jvm option that is required to enforce
start of the week = Monday in IsoCalendarDataProvider.
Adding a `feature` to yml test in order to skip running it in JDK8

commit that removed it 398c802
commit that backports SystemJvmOptions c4fbda3
relates 7.x backport of code that enforces CalendarDataProvider use #48349
2020-01-21 09:02:21 +01:00
Nhat Nguyen 43ed244a04
Account soft-deletes in FrozenEngine (#51192) (#51229)
Currently, we do not exclude soft-deleted documents when opening index
reader in the FrozenEngine.

Backport of #51192
2020-01-20 17:07:29 -05:00
zacharymorn dc02458dd6 Exclude unmapped fields from query max_clause limit (#49523)
Take into account of number of unmapped fields when calculating against limit.
Closes #49002
2020-01-20 13:44:33 +01:00
Armin Braun 694b8ab95d
Fix CorruptedBlobStoreRepository Test (#51128) (#51186)
The tests, when creating broken serialized blobs could randomly create
a sequence of bytes that is partially readable by the deserializer and then
not throw `IOException` but instead `ElasticsearchParseException`.
We should just handle these unexpected exceptions downstream properly and pass them
wrapped as `RepositoryException` to the listener to fix the test and keep the API consistent.
2020-01-18 14:12:55 +01:00
Jay Modi 107989df3e
Introduce hidden indices (#51164)
This change introduces a new feature for indices so that they can be
hidden from wildcard expansion. The feature is referred to as hidden
indices. An index can be marked hidden through the use of an index
setting, `index.hidden`, at creation time. One primary use case for
this feature is to have a construct that fits indices that are created
by the stack that contain data used for display to the user and/or
intended for querying by the user. The desire to keep them hidden is
to avoid confusing users when searching all of the data they have
indexed and getting results returned from indices created by the
system.

Hidden indices have the following properties:
* API calls for all indices (empty indices array, _all, or *) will not
  return hidden indices by default.
* Wildcard expansion will not return hidden indices by default unless
  the wildcard pattern begins with a `.`. This behavior is similar to
  shell expansion of wildcards.
* REST API calls can enable the expansion of wildcards to hidden
  indices with the `expand_wildcards` parameter. To expand wildcards
  to hidden indices, use the value `hidden` in conjunction with `open`
  and/or `closed`.
* Creation of a hidden index will ignore global index templates. A
  global index template is one with a match-all pattern.
* Index templates can make an index hidden, with the exception of a
  global index template.
* Accessing a hidden index directly requires no additional parameters.

Backport of #50452
2020-01-17 10:09:01 -07:00
Nik Everett 5299664ae3
"did you mean" for ObjectParser with top named (#51018) (#51165)
When you declare an ObjectParser with top level named objects like we do
with `significant_terms` we didn't support "did you mean". This fixes
that.

Relates #50938
2020-01-17 12:00:03 -05:00
Armin Braun e51b209dd3
Fix Infinite Retry Loop in loading RepositoryData (#50987) (#51093)
* Fix Infinite Retry Loop in loading RepositoryData

We were running into an infinite loop when trying to load corrupted (or otherwise un-loadable)
repository data for a repo that uses best effort consistency (e.g. that was just freshly mounted
as done in the test) because we kepy resetting to `-1` on `IOException`, listing and finding the broken
generation `N` and then interpreted the subsequent reset to `-1` as a concurrent change to the repository.
2020-01-16 21:08:35 +01:00
Nik Everett f6c89b4599
Move test of custom sig heuristic to plugin (#50891) (#51067)
This moves the testing of custom significance heuristic plugins from an
`ESIntegTestCase` to an example plugin. This is *much* more "real" and
can be used as an example for anyone that needs to actually build such a
plugin. The old test had testing concerns and the example all jumbled
together.
2020-01-16 14:49:12 -05:00
Zachary Tong e2ca93bad3 Mute GeoGridAggregatorTestCase#testBounds()
Tracking issue: https://github.com/elastic/elasticsearch/issues/51103
2020-01-16 10:28:10 -05:00
Marios Trivyzas fda25ed04a
Fix caching for PreConfiguredTokenFilter (#50912) (#51091)
The PreConfiguredTokenFilter#singletonWithVersion uses the version
internally for the token filter factories but it registers only one
instance in the cache and not one instance per version. This can lead
to exceptions like the one described in #50734 since the singleton is
created and cached using the version created of the first index
that is processed.

Remove the singletonWithVersion() methods and use the
elasticsearchVersion() methods instead.

Fixes: #50734
(cherry picked from commit 24e1858)
2020-01-16 13:58:02 +01:00
Martijn van Groningen 02dfd71efa
Backport: Add pipeline name to ingest metadata (#51050)
Backport: #50467

This commit adds the name of the current pipeline to ingest metadata.
This pipeline name is accessible under the following key: '_ingest.pipeline'.

Example usage in pipeline:
PUT /_ingest/pipeline/2
{
    "processors": [
        {
            "set": {
                "field": "pipeline_name",
                "value": "{{_ingest.pipeline}}"
            }
        }
    ]
}

Closes #42106
2020-01-16 10:50:47 +01:00
Zachary Tong 9eab87062c Bump version to 7.7.0 2020-01-15 10:12:14 -05:00
Yannick Welsch dc47b380c8 Block too many concurrent mapping updates (#51038)
Ensures that there are not too many concurrent dynamic mapping updates going out from the
data nodes to the master.

Closes #50670
2020-01-15 16:02:11 +01:00
Alan Woodward 0257de8c26
Emit warnings when index templates have multiple mappings (#50982)
Index templates created in the 5x line can still be present in the cluster state
through multiple upgrades, and may have more than one mapping defined. 8x
will stop supporting templates with multiple mappings, and we should emit
deprecation warnings in 7x clusters to give users a chance to update their
templates before upgrading.
2020-01-15 11:59:27 +00:00
Nik Everett fc5fde7950
Add "did you mean" to ObjectParser (#50938) (#50985)
Check it out:
```
$ curl -u elastic:password -HContent-Type:application/json -XPOST localhost:9200/test/_update/foo?pretty -d'{
  "dac": {}
}'

{
  "error" : {
    "root_cause" : [
      {
        "type" : "x_content_parse_exception",
        "reason" : "[2:3] [UpdateRequest] unknown field [dac] did you mean [doc]?"
      }
    ],
    "type" : "x_content_parse_exception",
    "reason" : "[2:3] [UpdateRequest] unknown field [dac] did you mean [doc]?"
  },
  "status" : 400
}
```

The tricky thing about implementing this is that x-content doesn't
depend on Lucene. So this works by creating an extension point for the
error message using SPI. Elasticsearch's server module provides the
"spell checking" implementation.
s
2020-01-14 17:53:41 -05:00
Yannick Welsch 4b0581f182 Remove custom metadata tool (#50813)
Adds a command-line tool to remove broken custom metadata from the cluster state.

Relates to #48701
2020-01-14 23:08:33 +01:00
Nik Everett a8aca6b2a0
Switch AggregationSpec to ContextParser (#50871) (#50980)
We seem to have settled on the `ContextParser` interface for parsing
stuff, mostly because `ObjectParser` implements it. We don't really
*need* the old `Aggregator.Parser` interface any more because it
duplicates `ContextParser` but with the arguments reversed.

This adds support to `AggregationSpec` to declare aggregation parsers
using `ContextParser`. This should integrate cleanly with
`ObjectParser`. It doesn't drop support for `Aggregator.Parser` or
change the plugin intrface at all so it *should* be safe to backport to
7.x. And we can remove `Aggregator.Parser` in a follow up which is only
targeted to 8.0.
2020-01-14 16:50:52 -05:00
Nik Everett 9a3d4db840
Begin moving date_histogram to offset rounding (backport of #50873) (#50978)
We added a new rounding in #50609 that handles offsets to the start and
end of the rounding so that we could support `offset` in the `composite`
aggregation. This starts moving `date_histogram` to that new offset.
2020-01-14 16:50:27 -05:00
Tal Levy 9ee2e11181
[7.x] Adds support for geo-bounds filtering in geogrid aggregations (#50996)
* Adds support for geo-bounds filtering in geogrid aggregations (#50002)

It is fairly common to filter the geo point candidates in
geohash_grid and geotile_grid aggregations according to some
viewable bounding box. This change introduces the option of
specifying this filter directly in the tiling aggregation.

This is even more relevant to `geo_shape` where the bounds will restrict
the shape to be within the bounds

this optional `bounds` parameter is parsed in an equivalent fashion to
the bounds specified in the geo_bounding_box query.
2020-01-14 11:18:46 -08:00
Armin Braun 16c07472e5
Track Snapshot Version in RepositoryData (#50930) (#50989)
* Track Snapshot Version in RepositoryData (#50930)

Add tracking of snapshot versions to RepositoryData to make BwC logic more efficient.
Follow up to #50853
2020-01-14 18:15:07 +01:00
Tim Brooks 6e7478b846
Allow proxy mode server name to be configured (#50951)
Currently, proxy mode allows a remote cluster connection to be setup by
expecting all open connections to be routed through an intermediate
proxy. The proxy must use some logic to ensure that the connections end
up on the correct remote cluster. One mechanism provided is that the
default distribution TLS implementations will forward the host component
of the configured address to the remote connection using the SNI
extension. This is limiting as it requires that the proxy be configured
in a way that always uses a valid hostname as the proxy address.

Instead, this commit adds an additional setting to allow the server_name
to be configured independently. This allows the proxy address to be
specified as a IP literal, but the server_name specified as an arbitrary
string which still must be a valid hostname. It also decouples the
server_name from the requirement of being a DNS resolvable domain.
2020-01-14 10:57:44 -06:00
Tim Brooks d8510be3d9
Revert "Send cluster name and discovery node in handshake (#48916)" (#50944)
This reverts commit 0645ee88e2.
2020-01-14 09:53:13 -06:00
Yannick Welsch f1c5031766 Fix queuing in AsyncLucenePersistedState (#50958)
The logic in AsyncLucenePersistedState was flawed, unexpectedly queuing up two update tasks
in parallel.
2020-01-14 15:04:28 +01:00
Yannick Welsch 91d7b446a0 Warn on slow metadata performance (#50956)
Has the new cluster state storage layer emit warnings in case metadata performance is very
slow.

Relates #48701
2020-01-14 15:04:28 +01:00
Alan Woodward 8c16725a0d Check for deprecations when analyzers are built (#50908)
Generally speaking, deprecated analysis components in elasticsearch will issue deprecation
warnings when they are first used. However, this means that no warnings are emitted when
indexes are created with deprecated components, and users have to actually index a document
to see warnings. This makes it much harder to see these warnings and act on them at
appropriate times.

This is worse in the case where components throw exceptions on upgrade. In this case, users
will not be aware of a problem until a document is indexed, instead of at index creation time.

This commit adds a new check that pushes an empty string through all user-defined analyzers
and normalizers when an IndexAnalyzers object is built for each index; deprecation warnings
and exceptions are now emitted when indexes are created or opened.

Fixes #42349
2020-01-14 13:52:02 +00:00
Yannick Welsch 22ba759e1f
Move metadata storage to Lucene (#50928)
* Move metadata storage to Lucene (#50907)

Today we split the on-disk cluster metadata across many files: one file for the metadata of each
index, plus one file for the global metadata and another for the manifest. Most metadata updates
only touch a few of these files, but some must write them all. If a node holds a large number of
indices then it's possible its disks are not fast enough to process a complete metadata update before timing out. In severe cases affecting master-eligible nodes this can prevent an election
from succeeding.

This commit uses Lucene as a metadata storage for the cluster state, and is a squashed version
of the following PRs that were targeting a feature branch:

* Introduce Lucene-based metadata persistence (#48733)

This commit introduces `LucenePersistedState` which master-eligible nodes
can use to persist the cluster metadata in a Lucene index rather than in
many separate files.

Relates #48701

* Remove per-index metadata without assigned shards (#49234)

Today on master-eligible nodes we maintain per-index metadata files for every
index. However, we also keep this metadata in the `LucenePersistedState`, and
only use the per-index metadata files for importing dangling indices. However
there is no point in importing a dangling index without any shard data, so we
do not need to maintain these extra files any more.

This commit removes per-index metadata files from nodes which do not hold any
shards of those indices.

Relates #48701

* Use Lucene exclusively for metadata storage (#50144)

This moves metadata persistence to Lucene for all node types. It also reenables BWC and adds
an interoperability layer for upgrades from prior versions.

This commit disables a number of tests related to dangling indices and command-line tools.
Those will be addressed in follow-ups.

Relates #48701

* Add command-line tool support for Lucene-based metadata storage (#50179)

Adds command-line tool support (unsafe-bootstrap, detach-cluster, repurpose, & shard
commands) for the Lucene-based metadata storage.

Relates #48701

* Use single directory for metadata (#50639)

Earlier PRs for #48701 introduced a separate directory for the cluster state. This is not needed
though, and introduces an additional unnecessary cognitive burden to the users.

Co-Authored-By: David Turner <david.turner@elastic.co>

* Add async dangling indices support (#50642)

Adds support for writing out dangling indices in an asynchronous way. Also provides an option to
avoid writing out dangling indices at all.

Relates #48701

* Fold node metadata into new node storage (#50741)

Moves node metadata to uses the new storage mechanism (see #48701) as the authoritative source.

* Write CS asynchronously on data-only nodes (#50782)

Writes cluster states out asynchronously on data-only nodes. The main reason for writing out
the cluster state at all is so that the data-only nodes can snap into a cluster, that they can do a
bit of bootstrap validation and so that the shard recovery tools work.
Cluster states that are written asynchronously have their voting configuration adapted to a non
existing configuration so that these nodes cannot mistakenly become master even if their node
role is changed back and forth.

Relates #48701

* Remove persistent cluster settings tool (#50694)

Adds the elasticsearch-node remove-settings tool to remove persistent settings from the on
disk cluster state in case where it contains incompatible settings that prevent the cluster from
forming.

Relates #48701

* Make cluster state writer resilient to disk issues (#50805)

Adds handling to make the cluster state writer resilient to disk issues. Relates to #48701

* Omit writing global metadata if no change (#50901)

Uses the same optimization for the new cluster state storage layer as the old one, writing global
metadata only when changed. Avoids writing out the global metadata if none of the persistent
fields changed. Speeds up server:integTest by ~10%.

Relates #48701

* DanglingIndicesIT should ensure node removed first (#50896)

These tests occasionally failed because the deletion was submitted before the
restarting node was removed from the cluster, causing the deletion not to be
fully acked. This commit fixes this by checking the restarting node has been
removed from the cluster.

Co-authored-by: David Turner <david.turner@elastic.co>

* fix tests

Co-authored-by: David Turner <david.turner@elastic.co>
2020-01-14 09:35:43 +01:00
Tim Brooks 50cb770315
Use default profile for remote connections (#50947)
Currently, the connection manager is configured with a default profile
for both the sniff and proxy connection stratgies. This profile
correctly reflects the expected number of connection (6 for sniff, 18
for proxy). This commit removes the proxy strategy usages of the per
connection attempt profile configuration.

Additionally, it refactors other unnecessary code around the connection
manager. The connection manager now can always be built inside the
remote connection.
2020-01-13 21:46:23 -06:00
Tim Brooks 27c2eb744e
Fix open/close race in ConnectionManagerTests (#50621)
Currently we reuse the same test connection for all connection attempts
in the testConcurrentConnectsAndDisconnects test. This means that if the
connection fails due to a pre-existing connection, the connection will
be closed impacting the state of all connection attempts. This commit
fixes the test, by returning a unique connection for each attempt.

Fixes #49903.
2020-01-13 18:43:18 -07:00
Nhat Nguyen fb32a55dd5 Deprecate synced flush (#50835)
A normal flush has the same effect as a synced flush on Elasticsearch 
7.6 or later. It's deprecated in 7.6 and will be removed in 8.0.

Relates #50776
2020-01-13 19:54:38 -05:00