CODEWITHSUNDEEP
elasticsearchcouchbase
shmish111
shmish111

Reputation: 3797

Couchbase XDCR Elasticsearch speed and deletions

We are thinking about implementing some sort of message cache which would hold onto the messages we send to our search index so we could persist while the index was down for an extended period of time (for example a complete re-index) then 're-apply' the messages. These messages are creations or updates of the documents we index. If space were cheap enough, with something as scalable as Couchbase we may even be able to hold all messages but I haven't done any sort of estimations of message size and quantity yet. Anyway, I suggested Couchbase + XDCR + Elasticsearch for this task as most of the work would be done automatically however there are 4 questions I have remaining:

  1. If we were implementing this as a cache, I would not want Elasticsearch to remove any documents that were not in Couchbase, is this possible to do (perhaps it is even the default behaviour)?

  2. Is it possible to apply some sort of versioning so that a document in the index is not over-written by an older version coming from Couchbase?

  3. If I were to add a new field to the index, I might need to re-index from the actual document datasource then re-apply all the messages stored in Couchbase. I may have 100 million documents in Elasticsearch and say 500,000 documents in Couchbase that I want to re-apply to Elasticsearch? What would the speed be like.

  4. Would I be able to apply any sort of logic in-between Couchbase and Elasticsearch?

Update:

So we store documents in an RDBMS as we need instant access to inserted docs plus some other stuff. We send limited versions of the document to a search engine via messages. If we want to add a field to the index we need to re-index the system from the RDBMS somehow. If we have this Couchbase message cache we could add the field to messages first, then switch off the indexing of old messages and re-index from the RDBMS. We could then switch back on the indexing of the messages and the entire 'queue' of messages would be indexed without having lost anything.

This system (if it worked) would remove the need for an MQ server, a message listener and make sure no documents were missing from the index.

The versioning would be necessary as we don't want to apply an 'update' to the index which actually contains a more recent document (not sure if this would ever happen now I think about it).

I appreciate it's probably not too great a job to implement points 1 and 4 by changing the Elasticsearch plugin code but I would like to confirm that the idea is reasonable first!

Upvotes: 2

Views: 784

Answers (1)

Tug Grall
Tug Grall

Reputation: 3510

The Couchbase-Elasticsearch integration today should be seen as an indexing engine for Couchbase. This means the index is "managed/controlled" by the data that are in Couchbase.

The XDCR is used to sent "all the events" to Elasticsearch. This means the index is update/delete every time a document (stored in Couchbase) is created, modified or deleted.

So "all the documents" stored into a Couchbase bucket are indexed into Elasticsearch.

Let's answer your questions one by one, based on the current implementation of the Couchbase-Elasticsearch.

  1. When a document is removed from Couchbase, the Elasticsearch index is update (entry removed).

  2. Not sure to understand the question. How an "older" version could come from Couchbase? Anyway once again everytime the document that is stored into Couchbase is modified, the index in Elasticsearch is updated.

  3. Not sure to understand where you want to add a new field? If this is into a document that is stored into Couchbase, when the document will be sent to Elasticsearch the index will be updated. But based on what I have said before : all document "stored" into Couchbase will be present in Elasticsearch index.

  4. Not with the plugin as it is today, but as you know it is an open source project so you can either add some logic to it or even contribute your ideas to the project ( https://github.com/couchbaselabs/elasticsearch-transport-couchbase )

So let me ask you more questions: - how do you inser the document into you application? (and where Couchbase? Elasticsearch?) - what are the types of documents? - what do you want to cache into Couchbase?

Upvotes: 1

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