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From Mark Robson <mar...@gmail.com>
Subject Re: Why are writes faster than reads?
Date Tue, 25 May 2010 23:05:53 GMT
On 25 May 2010 09:04, David Boxenhorn <david@lookin2.com> wrote:

> I have seen several off-hand mentions that writes are inherently faster
> than reads. Why is this so?
>

In addition to the points that other posters made, writes only need to go as
far as your battery-backed raid controller, whereas reads go all the way to
the disc, possibly quite a lot of times (to search a tree structure for the
right block). The client has no option but to wait for these.

For durability, you just need the data to be in battery-backed ram in the
controller, which is a pretty fast path, provided it has sufficient
throughput to get the blocks on to disc faster than they're being written to
(which should not be a problem for Cassandra's sequentially-written commit
log and sstable files)

Mark

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