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https://issues.apache.org/jira/browse/SOLR-1924?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12921919#action_12921919
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Jan Høydahl commented on SOLR-1924:
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In a multi node environment, it would also be useful to maintain state as to
whether a batch is replicated to the slaves. This is because in case of
disaster crash on a master, the feeding client may have got callback that a
batch is secured, but it was not yet replicated, i.e. the only copy was on the
now crashed master. The master should be able to keep track of whether at least
one replica has fetched a certain version of the index through the
ReplicationHandler. In this way, a client could choose to act on the
replication status instead of persisted status. The <STATUS> operation would
now return an additional state:
<replicated count="1">fooBar0000</replicated> <persisted count="2">fooBar0001
fooBar0002</persisted> <pending count="1">fooBar0003</pending>
> Solr's updateRequestHandler does not have a fast way of guaranteeing document
> delivery
> --------------------------------------------------------------------------------------
>
> Key: SOLR-1924
> URL: https://issues.apache.org/jira/browse/SOLR-1924
> Project: Solr
> Issue Type: Bug
> Affects Versions: 1.4
> Reporter: Karl Wright
>
> It is currently not possible, without performing a commit on every document,
> to use updateRequestHandler to guarantee delivery into the index of any
> document. The reason is that whenever Solr is restarted, some or all
> documents that have not been committed yet are dropped on the floor, and
> there is no way for a client of updateRequestHandler to know which ones this
> happened to.
> I believe it is not even possible to write a middleware-style layer that
> stores documents and performs periodic commits on its own, because the update
> request handler never ACKs individual documents on a commit, but merely
> everything it has seen since the last time Solr bounced. So you have this
> potential scenario:
> - middleware layer receives document 1, saves it
> - middleware layer receives document 2, saves it
> Now it's time for the commit, so:
> - middleware layer sends document 1 to updateRequestHandler
> - solr is restarted, dropping all uncommitted documents on the floor
> - middleware layer sends document 2 to updateRequestHandler
> - middleware layer sends COMMIT to updateRequestHandler, but solr adds only
> document 2 to the index
> - middleware believes incorrectly that it has successfully committed both
> documents
> An ideal solution would be for Solr to separate the semantics of commit (the
> index building variety) from the semantics of commit (the 'I got the
> document' variety). Perhaps this will involve a persistent document queue
> that will persist over a Solr restart.
> An alternative mechanism might be for updateRequestHandler to acknowledge
> specifically committed documents in its response to an explicit commit. But
> this would make it difficult or impossible to use autocommit usefully in such
> situations. The only other alternative is to require clients that need
> guaranteed delivery to commit on every document, with a considerable
> performance penalty.
> This ticket is related to LCF in that LCF is one of the clients that really
> needs some kind of guaranteed delivery mechanism.
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