# Issue with "Synced Flush" for Elasticsearch (ES) V 1.5.2

**URL:** <https://discuss.elastic.co/t/issue-with-synced-flush-for-elasticsearch-es-v-1-5-2/50237>\
**Category:** Elasticsearch\
**Created:** [May 17, 2016, 3:36pm UTC](https://discuss.elastic.co/t/issue-with-synced-flush-for-elasticsearch-es-v-1-5-2/50237 "2016-05-17T15:36:35Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![vikram\_yerneni](https://avatars.discourse-cdn.com/v4/letter/v/3ab097/32.png) [@vikram\_yerneni](https://discuss.elastic.co/u/vikram_yerneni)\
**Post date:** [May 17, 2016, 3:36pm UTC](https://discuss.elastic.co/t/issue-with-synced-flush-for-elasticsearch-es-v-1-5-2/50237/1 "2016-05-17T15:36:35Z")

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Folks,  
I am planning to upgrade my ES from 1.5.2 to 2.3.1 and I am going through regular upgrade process. I disabled the Shard allocation and I am getting an issue when I am trying to perform the Synced Flush (POST /\_flush/synced). I am getting the below error:

{  
"error": "InvalidIndexNameException[[\_flush] Invalid index name [_flush], must not start with '_']",  
"status": 400  
}

So, I did some research and found a work around (sort of) for this issue (from [Synced Flush Causes Node to Restart](https://discuss.elastic.co/t/synced-flush-causes-node-to-restart/24220/13)) and tried to target an individual index (index name: test01) rather than all indexes and I got this error:

{  
"error": "RemoteTransportException[[test001][inet[/100.82.21.7:9303]][indices:data/write/index]]; nested: InvalidTypeNameException[mapping type name [_flush] can't start with '_']; ",  
"status": 400  
}

Not sure if the ES 1.5.2 has any issues with the Synced Flush API call or if I need additional plugins involved in my current ES 1.5.2 setup!!

Any inputs will be appreciated..

Thanks  
Vikram Y

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**Author:** ![Christian\_Dahlqvist](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/christian_dahlqvist/32/4617_2.png) [@Christian\_Dahlqvist](https://discuss.elastic.co/u/Christian_Dahlqvist)\
**Post date:** [May 17, 2016, 3:50pm UTC](https://discuss.elastic.co/t/issue-with-synced-flush-for-elasticsearch-es-v-1-5-2/50237/2 "2016-05-17T15:50:19Z")

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I believe synced flush was introduced in [Elasticsearch 1.6.0](https://www.elastic.co/blog/elasticsearch-1-6-0-released), so don't think it is available in 1.5.2, which would explain the error you are getting.

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**Author:** ![vikram\_yerneni](https://avatars.discourse-cdn.com/v4/letter/v/3ab097/32.png) [@vikram\_yerneni](https://discuss.elastic.co/u/vikram_yerneni)\
**Post date:** [May 17, 2016, 4:05pm UTC](https://discuss.elastic.co/t/issue-with-synced-flush-for-elasticsearch-es-v-1-5-2/50237/3 "2016-05-17T16:05:04Z")

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Yes Christian.. I just saw this in one of the blog post ([Replicas synchronization](https://discuss.elastic.co/t/replicas-synchronization/37091)).  
Well, if thats the case do we know a best possible way to perform the upgrade to newer version of ES without the "synced flush" process? Or is there a different process of upgrading these older versions of ES..??

Please do add your points..

Thanks  
Vikram Y

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<div class="post-metadata">

**Author:** ![Christian\_Dahlqvist](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/christian_dahlqvist/32/4617_2.png) [@Christian\_Dahlqvist](https://discuss.elastic.co/u/Christian_Dahlqvist)\
**Post date:** [May 17, 2016, 4:15pm UTC](https://discuss.elastic.co/t/issue-with-synced-flush-for-elasticsearch-es-v-1-5-2/50237/4 "2016-05-17T16:15:38Z")

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Have you read this [blog post](https://www.elastic.co/blog/key-point-to-be-aware-of-when-upgrading-from-elasticsearch-1-to-2)? Make sure that you run the migration plugin to identify potential issues if you have not already done so.

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**Author:** ![vikram\_yerneni](https://avatars.discourse-cdn.com/v4/letter/v/3ab097/32.png) [@vikram\_yerneni](https://discuss.elastic.co/u/vikram_yerneni)\
**Post date:** [May 17, 2016, 4:21pm UTC](https://discuss.elastic.co/t/issue-with-synced-flush-for-elasticsearch-es-v-1-5-2/50237/5 "2016-05-17T16:21:21Z")

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Thanks dude.. I haven'e gone through this.. Let me.. I will post questions back if I get any..

Thanks again..  
Vikram Y

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [July 5, 2017, 10:50pm UTC](https://discuss.elastic.co/t/issue-with-synced-flush-for-elasticsearch-es-v-1-5-2/50237/6 "2017-07-05T22:50:56Z")

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