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https://issues.apache.org/jira/browse/OAK-4412?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15350537#comment-15350537
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Chetan Mehrotra commented on OAK-4412:
--------------------------------------
The approach proposed here is bit different. So would try to explain again
Oak provides a MVCC storage and currently Lucene indexes are updated on one of
the cluster node via an asynchronous task. This task compares the NodeStates
between previous last indexed state and current head state and indexes the
changed content. Once done the updated index state is committed. This change is
then picked by other cluster node and they update there local copy of index to
latest state.
Due to the async nature of this task the index state lags the latest repository
state.
To address this lag this Hybrid index approach is proposed. Under this
# A periodic task keeps the persisted lucene index (L0) upto date as explained
before. Lets say the index is upto date till revision R0-1 i.e. index content
match the repository state at revision R1
# Now lets say for a cluster node N1 the current head is R1-1. Here R1-1 >
R0-1.
# On each cluster node we would have an observor which maintains a "local"
index (L1) and "only" indexes content changed between R0-1 and R1-1
# Any query would then be run against both L0 and L1 and results would be joined
Note that each cluster node would have its own copy of the "local" index and
whose state might differ from other cluster nodes. It does not involve any
replication of the in memory index, instead rely on fact that each cluster node
maintains it own copy of local index for the respective delta between there
current head state and last indexed state
With this setup and with sticky session enabled it should be possible to
provide more accurate query result for changes happening on that cluster node.
So this is all in theory which still needs to validated and see how it
performs!!
> Lucene hybrid index
> -------------------
>
> Key: OAK-4412
> URL: https://issues.apache.org/jira/browse/OAK-4412
> Project: Jackrabbit Oak
> Issue Type: Improvement
> Components: lucene
> Reporter: Tomek Rękawek
> Assignee: Tomek Rękawek
> Fix For: 1.6
>
> Attachments: OAK-4412.patch
>
>
> When running Oak in a cluster, each write operation is expensive. After
> performing some stress-tests with a geo-distributed Mongo cluster, we've
> found out that updating property indexes is a large part of the overall
> traffic.
> The asynchronous index would be an answer here (as the index update won't be
> made in the client request thread), but the AEM requires the updates to be
> visible immediately in order to work properly.
> The idea here is to enhance the existing asynchronous Lucene index with a
> synchronous, locally-stored counterpart that will persist only the data since
> the last Lucene background reindexing job.
> The new index can be stored in memory or (if necessary) in MMAPed local
> files. Once the "main" Lucene index is being updated, the local index will be
> purged.
> Queries will use an union of results from the {{lucene}} and
> {{lucene-memory}} indexes.
> The {{lucene-memory}} index, as a local stored entity, will be updated using
> an observer, so it'll get both local and remote changes.
> The original idea has been suggested by [~chetanm] in the discussion for the
> OAK-4233.
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