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From Edward Capriolo <>
Subject Re: unable to read saved rowcache from disk
Date Wed, 14 Nov 2012 07:13:41 GMT

A negative side-effect of a large row-cache is start-up time. The
periodic saving of the row cache information only saves the keys that
are cached; the data has to be pre-fetched on start-up. On a large
data set, this is probably going to be seek-bound and the time it
takes to warm up the row cache will be linear with respect to the row
cache size (assuming sufficiently large amounts of data that the seek
bound I/O is not subject to optimization by disks)

Assuming a row cache 15MB and the average row is 300 bytes, that could
be 50,000 entries. 4 hours seems like a long time to read back 50K
entries. Unless the source table was very large and you can only do a
small number / reads/sec.

On Tue, Nov 13, 2012 at 9:47 PM, Manu Zhang <> wrote:
> "incorrect"... what do you mean? I think it's only 15MB, which is not big.
> On Wed, Nov 14, 2012 at 10:38 AM, Edward Capriolo <>
> wrote:
>> Yes the row cache "could be" incorrect so on startup cassandra verify they
>> saved row cache by re reading. It takes a long time so do not save a big row
>> cache.
>> On Tuesday, November 13, 2012, Manu Zhang <> wrote:
>> > I have a rowcache provieded by SerializingCacheProvider.
>> > The data that has been read into it is about 500MB, as claimed by
>> > jconsole. After saving cache, it is around 15MB on disk. Hence, I suppose
>> > the size from jconsole is before serializing.
>> > Now while restarting Cassandra, it's unable to read saved rowcache back.
>> > By "unable", I mean around 4 hours and I have to abort it and remove cache
>> > so as not to suspend other tasks.
>> > Since the data aren't huge, why Cassandra can't read it back?
>> > My Cassandra is 1.2.0-beta2.

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