ES default - async or sync

daa_qqu · September 7, 2014, 1:38am

What is the default replication policy in Elasticsearch? Does it push
changes to replicas asynchronously or synchronously? Or does it use
different mode with different operations.
asynchronous replication
http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/docs-index_.html#index-replication

By default, the index operation only returns after all shards within the
replication group have indexed the document (sync replication).
optimistic concurrency control
http://www.elasticsearch.org/guide/en/elasticsearch/guide/current/optimistic-concurrency-control.html#optimistic-concurrency-control
Elasticsearch is distributed. When documents are created, updated or
deleted, the new version of the document has to be replicated to other
nodes in the cluster. Elasticsearch is also asynchronous and concurrent

This book Ealsticsearch Definitive Guide, states under 'Creating, indexing
and deleting' that "...default value for replication is synchronous". When
discussing 'update' API it is stated that "...these changes are forwarded
to the replica shards asynchronously...."

github.com

elastic/elasticsearch-definitive-guide/blob/master/040_Distributed_CRUD/15_Create_index_delete.asciidoc

[[distrib-write]]
=== Creating, Indexing, and Deleting a Document

Create, index, and delete((("documents", "creating, indexing, and deleting"))) requests are _write_ operations,((("write operations"))) which must be
successfully completed on the primary shard before they can be copied to any
associated replica shards, as shown in <<img-distrib-write>>.

[[img-distrib-write]]
.Creating, indexing, or deleting a single document
image::images/elas_0402.png["Creating, indexing or deleting a single document"]

Here is the sequence ((("primary shards", "creating, indexing, and deleting a document")))((("replica shards", "creating, indexing, and deleting a document")))of steps necessary to successfully create, index, or
delete a document on both the primary and any replica shards:

1. The client sends a create, index, or delete request to `Node 1`.

2. The node uses the document's `_id` to determine that the document
   belongs to shard `0`. It forwards the request to `Node 3`,
   where the primary copy of shard `0` is currently allocated.

This file has been truncated. show original

replication

*** The default value for replication is sync. This causes the primary
shard to wait for successful responses from the replica shards before
returning.

github.com

elastic/elasticsearch-definitive-guide/blob/master/040_Distributed_CRUD/25_Partial_updates.asciidoc

=== Partial Updates to a Document

The `update` API , as shown in <<img-distrib-update>>, combines the read and((("updating documents", "partial updates")))((("documents", "partial updates"))) write patterns explained previously.

[[img-distrib-update]]
.Partial updates to a document
image::images/elas_0404.png["Partial updates to a document"]

Here is the sequence of steps used to perform a partial update on  a
document:

1. The client sends an update request to `Node 1`.

2. It forwards the request to `Node 3`, where the primary shard is allocated.

3. `Node 3` retrieves the document from the primary shard, changes the JSON
   in the `_source` field, and tries to reindex the document on the primary
   shard. If the document has already been changed by another process, it
   retries step 3 up to `retry_on_conflict` times, before giving up.

This file has been truncated. show original

Document based replication

When a primary shard forwards changes to its replica shards, it doesn’t
forward the update request. Instead it forwards the new version of the full
document. ***Remember that these changes are forwarded to the replica
shards asynchronously and there is no guarantee that they will arrive in
the same order that they were sent.

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Clinton_Gormley · September 7, 2014, 8:31am

Hiya

OK I see where the confusion is coming in. I used the word asynchronously
in slightly different contexts there. I will try to reword in the
Definitive Guide.

Replication is sync by default, in other words: the primary waits for
indexing to happen on the replica before it returns to the user. That
said, lots of these processes happen at the same time, so sending the
document to the replica is asynchronous. It doesn't send a change then
wait for the response before sending the next one. This all happens in
parallel.

Does that make it clearer?

On 7 September 2014 03:38, daa qqu daaqqu@gmail.com wrote:

What is the default replication policy in Elasticsearch? Does it push
changes to replicas asynchronously or synchronously? Or does it use
different mode with different operations.
asynchronous replication
http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/docs-index_.html#index-replication

By default, the index operation only returns after all shards within the
replication group have indexed the document (sync replication).
optimistic concurrency control
http://www.elasticsearch.org/guide/en/elasticsearch/guide/current/optimistic-concurrency-control.html#optimistic-concurrency-control
Elasticsearch is distributed. When documents are created, updated or
deleted, the new version of the document has to be replicated to other
nodes in the cluster. Elasticsearch is also asynchronous and concurrent

This book Ealsticsearch Definitive Guide, states under 'Creating, indexing
and deleting' that "...default value for replication is synchronous". When
discussing 'update' API it is stated that "...these changes are forwarded
to the replica shards asynchronously...."

https://github.com/elasticsearch/elasticsearch-definitive-guide/blob/master/040_Distributed_CRUD/15_Create_index_delete.asciidoc
replication

*** The default value for replication is sync. This causes the primary
shard to wait for successful responses from the replica shards before
returning.

https://github.com/elasticsearch/elasticsearch-definitive-guide/blob/master/040_Distributed_CRUD/25_Partial_updates.asciidoc

Document based replication

When a primary shard forwards changes to its replica shards, it doesn’t
forward the update request. Instead it forwards the new version of the full
document. ***Remember that these changes are forwarded to the replica
shards asynchronously and there is no guarantee that they will arrive in
the same order that they were sent.

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daa_qqu · September 8, 2014, 2:05am

Wow! Straight from the author. Thank you Clinton!! Makes sense now.

On Sun, Sep 7, 2014 at 1:31 AM, Clinton Gormley clint@traveljury.com
wrote:

Hiya

OK I see where the confusion is coming in. I used the word asynchronously
in slightly different contexts there. I will try to reword in the
Definitive Guide.

Replication is sync by default, in other words: the primary waits for
indexing to happen on the replica before it returns to the user. That
said, lots of these processes happen at the same time, so sending the
document to the replica is asynchronous. It doesn't send a change then
wait for the response before sending the next one. This all happens in
parallel.

Does that make it clearer?

On 7 September 2014 03:38, daa qqu daaqqu@gmail.com wrote:

What is the default replication policy in Elasticsearch? Does it push
changes to replicas asynchronously or synchronously? Or does it use
different mode with different operations.
asynchronous replication
http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/docs-index_.html#index-replication

By default, the index operation only returns after all shards within the
replication group have indexed the document (sync replication).
optimistic concurrency control
http://www.elasticsearch.org/guide/en/elasticsearch/guide/current/optimistic-concurrency-control.html#optimistic-concurrency-control
Elasticsearch is distributed. When documents are created, updated or
deleted, the new version of the document has to be replicated to other
nodes in the cluster. Elasticsearch is also asynchronous and concurrent

This book Ealsticsearch Definitive Guide, states under 'Creating,
indexing and deleting' that "...default value for replication is
synchronous". When discussing 'update' API it is stated that "...these
changes are forwarded to the replica shards asynchronously...."

https://github.com/elasticsearch/elasticsearch-definitive-guide/blob/master/040_Distributed_CRUD/15_Create_index_delete.asciidoc
replication

*** The default value for replication is sync. This causes the primary
shard to wait for successful responses from the replica shards before
returning.

https://github.com/elasticsearch/elasticsearch-definitive-guide/blob/master/040_Distributed_CRUD/25_Partial_updates.asciidoc

Document based replication

When a primary shard forwards changes to its replica shards, it doesn’t
forward the update request. Instead it forwards the new version of the full
document. ***Remember that these changes are forwarded to the replica
shards asynchronously and there is no guarantee that they will arrive in
the same order that they were sent.

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ElasticSearch_Users_ · February 2, 2015, 2:26pm

Hi Clinton,

Is using async NOT recommonded? The Definitive Guild says, "This option is
mentioned specifically to advise against using it. The default sync replication
allows Elasticsearch to exert back pressure on whatever system is feeding
it with data. With async replication, it is possible to overload
Elasticsearch by sending too many requests without waiting for their
completion."

Also, if the indexes has not being updated in the replica, could the
query only be sent to the replica and elasticsearch return not found?

On Sunday, 7 September 2014 04:31:30 UTC-4, Clinton Gormley wrote:

Hiya

OK I see where the confusion is coming in. I used the word asynchronously
in slightly different contexts there. I will try to reword in the
Definitive Guide.

Replication is sync by default, in other words: the primary waits for
indexing to happen on the replica before it returns to the user. That
said, lots of these processes happen at the same time, so sending the
document to the replica is asynchronous. It doesn't send a change then
wait for the response before sending the next one. This all happens in
parallel.

Does that make it clearer?

On 7 September 2014 03:38, daa qqu <daa...@gmail.com <javascript:>> wrote:

What is the default replication policy in Elasticsearch? Does it push
changes to replicas asynchronously or synchronously? Or does it use
different mode with different operations.
asynchronous replication
http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/docs-index_.html#index-replication

By default, the index operation only returns after all shards within the
replication group have indexed the document (sync replication).
optimistic concurrency control
http://www.elasticsearch.org/guide/en/elasticsearch/guide/current/optimistic-concurrency-control.html#optimistic-concurrency-control
Elasticsearch is distributed. When documents are created, updated or
deleted, the new version of the document has to be replicated to other
nodes in the cluster. Elasticsearch is also asynchronous and concurrent

This book Ealsticsearch Definitive Guide, states under 'Creating,
indexing and deleting' that "...default value for replication is
synchronous". When discussing 'update' API it is stated that "...these
changes are forwarded to the replica shards asynchronously...."

https://github.com/elasticsearch/elasticsearch-definitive-guide/blob/master/040_Distributed_CRUD/15_Create_index_delete.asciidoc
replication

*** The default value for replication is sync. This causes the primary
shard to wait for successful responses from the replica shards before
returning.

https://github.com/elasticsearch/elasticsearch-definitive-guide/blob/master/040_Distributed_CRUD/25_Partial_updates.asciidoc

Document based replication

When a primary shard forwards changes to its replica shards, it doesn’t
forward the update request. Instead it forwards the new version of the full
document. ***Remember that these changes are forwarded to the replica
shards asynchronously and there is no guarantee that they will arrive in
the same order that they were sent.

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