[Solr Wiki] Update of "CommitWithin" by JanHoydahl

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The "CommitWithin" page has been changed by JanHoydahl:
http://wiki.apache.org/solr/CommitWithin

Comment:
First documentation

New page:
There are multiple commit strategies in Solr. The most known is explicit <commit>s from the client. Then you have AutoCommit, configured in solrconfig.xml, which lets Solr automatically commit <add>s after a certain time or number of documents, and finally there may be a behind-the-scenes commit when the input buffer gets full.

== What is it ==
'''CommitWithin''' is a commit strategy introduced in Solr 1.4, which lets the client ask Solr to make sure this <add> gets committed within a certain time. This leaves the control of when to do the commit to Solr itself, minimizing number of commits to a minimum while still trying to fulfill the update latency requirements. If I say <add commitWithin=10000> (in an XMLUpdateRequestHandler update), that tells Solr to make sure the document gets committed within 10000ms, i.e. 10s. I can then continue to add other documents within those 10 seconds (possibly with other commitWithin values), and Solr will automatically do a <commit> when the oldest <add> batch in the buffer gets due.

== Ways to do commitWithin ==
There are multiple ways to convey the commitWithin information to Solr.

=== In XML or JSON documents ===
You can specify a commitWithin parameter directly on the <add> tag, see [[http://wiki.apache.org/solr/UpdateXmlMessages#Optional_attributes_for_.22add.22|UpdateXmlMessages]] for an example

=== SolrJ ===
In SolrJ you may optionally give a commitWithin value on the add() call, e.g. server.add(mySolrInputDocument, 10000); <!> [[Solr3.4]]

In earlier versions you need to construct an AddUpdateCommand and then set the commitWithin attribute on that - a little more work. Example:
{{{
    UpdateRequest req = new UpdateRequest();
    req.add(mySolrInputDocument);
    req.setCommitWithin(10000);
    req.process(this);
}}}

=== Update Request parameter ===
All UpdateRequestHandlers support the commitWithin request parameter as of <!> [[Solr3.4]]. This means that you may tell Solr to use a commitWithin value for the whole request. This is handy especially for [[CSVUpdateRequestHandler]] or ExtractingRequestHandler, which has no other way of conveying that information. An example using curl to push a PDF document, saying it should be committed within 10s:
{{{
curl http://localhost:8983/solr/update/extract?literal.id=123&commitWithin=10000
       -H "Content-Type: application/pdf" --data-binary @file.pdf
}}}