
MongoDB Performance for more data than memory - chaostheory
http://www.colinhowe.co.uk/2011/02/23/mongodb-performance-for-data-bigger-than-memor/
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antirez
I don't think it's a MongoDB fault, it is simply true with everything that is
serving data bigger than available memory. Of course there is also no solution
to the problem as the disk is slower... unless your working set still fits you
are going to pay the added latency.

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thibaut_barrere
One question I really have is: for the exact same dataset, how much RAM is
used to handle it with MongoDB, Redis, MySQL, or even a column-based store.

If someone has such a benchmark already, I'd love to read it.

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otterley
There's no way to know, really. When you mmap() backing stores into process
memory as MongoDB and Redis do, the OS takes care of paging activity for you.
And they get to compete with other processes on the system for memory pages.

InnoDB (MySQL) allows you to fix its buffer pool in RAM, so it makes decisions
as to which pages to buffer instead of the OS. Sometimes it makes better
decisions, sometimes it doesn't.

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nkurz
While MongoDB does this, I don't think that Redis takes this approach. In
theory, it manages the memory itself, reading from disk into its own cache. In
practice, I worry that it might end up competing with the system, leading to
"full memory" like conditions far before memory is actually exhausted. Thus my
interest in how it performs in a simple real life test like this.

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antirez
No mmap in Redis indeed.

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otterley
My mistake.

