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From aaron morton <aa...@thelastpickle.com>
Subject Re: row cache re-fill very slow
Date Mon, 19 Nov 2012 21:00:56 GMT
> i was just wondering if anyone else is experiencing very slow ( ~ 3.5 MB/sec ) re-fill
of the row cache at start up.
It was mentioned the other day.  

What version are you on ? 
Do you know how many rows were loaded ? When complete it will log a message with the pattern


"completed loading (%d ms; %d keys) row cache for %s.%s"

> How is the "saved row cache file" processed?

In Version 1.1, after the SSTables have been opened the keys in the saved row cache are read
one at a time and the whole row read into memory. This is a single threaded operation. 

In 1.2 reading the saved cache is still single threaded, but reading the rows goes through
the read thread pool so is in parallel.

In both cases I do not believe the cache is stored in token (or key) order. 

> ( Admittedly whatever is going on is still much more preferable to starting with a cold
row cache )

row_cache_keys_to_save in yaml may help you find a happy half way point. 

Cheers


-----------------
Aaron Morton
Freelance Cassandra Developer
New Zealand

@aaronmorton
http://www.thelastpickle.com

On 20/11/2012, at 3:17 AM, Andras Szerdahelyi <andras.szerdahelyi@ignitionone.com> wrote:

> Hey list,
> 
> i was just wondering if anyone else is experiencing very slow ( ~ 3.5 MB/sec ) re-fill
of the row cache at start up. We operate with a large row cache ( 10-15GB currently ) and
we already measure startup times in hours :-)
> 
> How is the "saved row cache file" processed? Are the cached row keys simply iterated
over and their respective rows read from SSTables - possibly creating random reads with small
enough sstable files, if the keys were not stored in a manner optimised for a quick re-fill
? -  or is there a smarter algorithm ( i.e. scan through one sstable at a time, filter rows
that should be in row cache )  at work and this operation is purely disk i/o bound ?
> 
> ( Admittedly whatever is going on is still much more preferable to starting with a cold
row cache )
> 
> thanks!
> Andras
> 
> 
> 
> Andras Szerdahelyi
> Solutions Architect, IgnitionOne | 1831 Diegem E.Mommaertslaan 20A
> M: +32 493 05 50 88 | Skype: sandrew84
> 
> 
> <C4798BB9-9092-4145-880B-A72C6B7AF9A4[41].png>
> 
> 


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