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From shimi <>
Subject disks and data files
Date Mon, 13 Dec 2010 11:29:44 GMT
I am reading the kafka design documentation ( and I came across this (under
constant time suffices) :

Intuitively a persistent queue could be built on simple reads and appends to
files as is commonly the case with logging solutions. Though this structure
would not support the rich semantics of a BTree implementation, but it has
the advantage that all operations are O(1) and reads do not block writes or
each other. This has obvious performance advantages since the performance is
completely decoupled from the data size--one server can now take full
advantage of a number of cheap, low-rotational speed 1+TB SATA drives.
Though they have poor seek performance, these drives often have comparable
performance for large reads and writes at 1/3 the price and 3x the capacity.

It is right to say that Cassandra takes advantage of this? the commit log
write is using append and sstables are only read after they were written.


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