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    <p>it's probably best to do this in the shell, conciously!, because you could cause havoc if you accidentally start such a command at the wrong moment and on the wrong instance.</p> <p>Most importantly: <strong>do this offline on an extra slave instance</strong> if you add an index on an existing DB! For large data sets, building an index can take hours, even days!</p> <p>see also:</p> <p><a href="http://www.mongodb.org/display/DOCS/Indexes" rel="nofollow">http://www.mongodb.org/display/DOCS/Indexes</a></p> <p><a href="http://www.javabeat.net/articles/print.php?article_id=353" rel="nofollow">http://www.javabeat.net/articles/print.php?article_id=353</a></p> <p><a href="http://www.mongodb.org/display/DOCS/Indexing+as+a+Background+Operation" rel="nofollow">http://www.mongodb.org/display/DOCS/Indexing+as+a+Background+Operation</a></p> <p><a href="http://nosql.mypopescu.com/post/1312926692/mongodb-indexes-and-indexing" rel="nofollow">http://nosql.mypopescu.com/post/1312926692/mongodb-indexes-and-indexing</a></p> <p>If you have a large data set, make sure to read up on the <strong>4square outage</strong> last year..!!</p> <p><a href="http://www.infoq.com/news/2010/10/4square_mongodb_outage" rel="nofollow">http://www.infoq.com/news/2010/10/4square_mongodb_outage</a></p> <p><a href="http://blog.foursquare.com/2010/10/05/so-that-was-a-bummer/" rel="nofollow">http://blog.foursquare.com/2010/10/05/so-that-was-a-bummer/</a></p> <p><a href="http://highscalability.com/blog/2010/10/15/troubles-with-sharding-what-can-we-learn-from-the-foursquare.html" rel="nofollow">http://highscalability.com/blog/2010/10/15/troubles-with-sharding-what-can-we-learn-from-the-foursquare.html</a></p> <hr> <p>one of the main reasons for not wanting to put indexing in a script or config file of some sort is that in MongoDB the index operation is blocking(!) -- that means MongoDB will stop other operations on the database from proceeding until the indexing is completed. Just imagine an innocent change in the code, requiring a new index to improve performance -- and this change is carelessly checked-in and deployed to production ... and suddenly your production MongoDB is feezing up for your app-server, because MongoDB is internally adding the new index <strong>first</strong> before doing anything else... outch! Apparently that has happened to a couple of folks, that's why they keep reminding people at the MongoDB conferences to be careful to not 'programmatically' require indexes.</p> <p>New versions of MongoDB allow background indexing -- you should always do that e.g. db.yourcollection.ensureIndex(..., {background: true})</p> <p>otherwise, not-so-fun stuff happens:</p> <p><a href="https://jira.mongodb.org/browse/SERVER-1341" rel="nofollow">https://jira.mongodb.org/browse/SERVER-1341</a></p> <p><a href="https://jira.mongodb.org/browse/SERVER-3067" rel="nofollow">https://jira.mongodb.org/browse/SERVER-3067</a></p>
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    1. POWhen/Where is the best-practices time/place to configure a MongoDB "schema"?
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    1. POWhen/Where is the best-practices time/place to configure a MongoDB "schema"?
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    1. COAre there any tools for managing or keeping track of this? Is the recommended work flow really just login into the shell and run the commands?
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    2. CO@Zach: I was at several of the MongoDB conferences.. and at several talks they cautioned to not accidentally trigger an index operation.. see my comment at the end of the post. You should talk to MongoDB customer support!
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    3. CO@Zach, think of indexes and shard keys as an admin function rather than a code function. A shard key can only be set once and indexes on large data are very difficult to change. As to the workflow, one could ponder a Ruby-style "migration" script, but there's no real standard here either. Frankly, with big data, indexes are big deals and best left to the admin. (of course, you could use an admin UI, you don't *have* to use the shell)
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