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Memory mapped files are nice, but once the mapped file starts to get much bigger than the physical memory pages the operating system can allocate, it starts to
by antirez 17y ago
Memory mapped files are nice, but once the mapped file starts to get much bigger than the physical memory pages the operating system can allocate, it starts to be asymptotically the same as accessing the filesystem from the point of view of latency, so indeed for datasets considerably bigger than RAM it is not possible to be as fast as memcached. Not a MongoDB limit, but a nature-imposed limit :)
- amix 17y agoI have had some bad experiences with memory mapped databases (particularly Berkeley DB and Tokyo Tyrant) - both these seem to be very greedy with IO writes when one starts to have lots of data and lots of updates. I think Reddit experienced a similar problem (as memcachedb is based on Berkeley DB). Does anybody know what Cassandra does?
- uggedal 17y agoTake a look at http://wiki.apache.org/cassandra/MemtableThresholds http://wiki.apache.org/cassandra/MemtableThresholds and http://wiki.apache.org/cassandra/ArchitectureOverview#Write_path http://wiki.apache.org/cassandra/ArchitectureOverview#Write_... for the specifics.