Saturday, February 06
Mongo Fail!
MongoDB ran out of memory and crashed during benchmarking. I headed off to look for the appropriate parameters to tune its memory consumption, and discovered that there aren't any.
MongoDB uses memory-mapped files for storage - as far as I can tell, it maps them in, and then puts all its structures in them, directly to memory, relying on the operating system to handle paging. On OpenVZ, that approach seems unlikely to work. And without at least a synchronous recovery log, it seems destined to destroy your database sooner or later anyway.
So, nice features, shame about the functionality.
Sigh.
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MongoDB ran out of memory and crashed during benchmarking. I headed off to look for the appropriate parameters to tune its memory consumption, and discovered that there aren't any.
MongoDB uses memory-mapped files for storage - as far as I can tell, it maps them in, and then puts all its structures in them, directly to memory, relying on the operating system to handle paging. On OpenVZ, that approach seems unlikely to work. And without at least a synchronous recovery log, it seems destined to destroy your database sooner or later anyway.
So, nice features, shame about the functionality.
Sigh.
Posted by: Pixy Misa at
02:41 PM
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Not sure why you had a problem, we aren't seeing this in general. Could you send the benchmark or post on http://groups.google.com/group/mongodb-user/, would like to fix.
Generally, we have seem many folks using MongoDB with databases far larger than RAM - for example 1TB in size.
Generally, we have seem many folks using MongoDB with databases far larger than RAM - for example 1TB in size.
Posted by: dm at Monday, February 08 2010 01:48 AM (Wi27I)
2
Thanks for the note, dm. Yes, I'll write up all the details and post on the user group.
It's quite possible that it's partly to do with running under OpenVZ, which has different out-of-memory behaviour than a physical Linux server or a full virtual machine.
It's quite possible that it's partly to do with running under OpenVZ, which has different out-of-memory behaviour than a physical Linux server or a full virtual machine.
Posted by: Pixy Misa at Monday, February 08 2010 01:59 AM (PiXy!)
45kb generated in CPU 0.0267, elapsed 0.1253 seconds.
56 queries taking 0.1152 seconds, 340 records returned.
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56 queries taking 0.1152 seconds, 340 records returned.
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