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From "Slater, David M." <David.Sla...@jhuapl.edu>
Subject RE: 0% Data Cache Hit Rate
Date Tue, 12 Mar 2013 20:24:55 GMT
I didn't up the cache size. Are the defaults tuned to running just the metatable data cache?

To "decide which tables you want to use that memory", is there an additional property to set?
tserver.cache.data.size you can set on a per-tserver basis, but how do you do it on a per
table basis? 

-----Original Message-----
From: Keith Turner [mailto:keith@deenlo.com] 
Sent: Tuesday, March 12, 2013 2:04 PM
To: user@accumulo.apache.org
Subject: Re: 0% Data Cache Hit Rate

On Tue, Mar 12, 2013 at 11:46 AM, Slater, David M.
<David.Slater@jhuapl.edu> wrote:
> Thanks Keith,
>
> I checked, and the values were all default. (cache block disabled)
>
> Turning them on, however, turned the data cache hit rate down to single digits for all
of the data nodes. I'm guessing that the queries I am running, since they need to go through
so much data, cannot be cached well, and that the high percentages I was getting before were
due to the use metatable data cache (since that is enabled by default).

That sounds correct.  Did you up the cache size?

>
> Since data caching is disabled by default, I assume that there are downsides to using
it. Is this primarily memory footprint?

Yeah, primarily memory.   Being able to enable/disable it allows you
to decide which tables you want to use that memory.

>
> Regards,
> David
>
> -----Original Message-----
> From: Keith Turner [mailto:keith@deenlo.com]
> Sent: Monday, March 11, 2013 3:02 PM
> To: user@accumulo.apache.org
> Subject: Re: 0% Data Cache Hit Rate
>
> You may need to set the following property to true for the table.
> This enables caching data for a table.  It defaults to false.
>
> table.cache.block.enable
>
> Also take a look at the following props.  These determine how much memory a tserver uses
for caching.
>
> tserver.cache.data.size
> tserver.cache.index.size
>
> The following props enables caching rfile indexes for a table, it defaults to true.
>
> table.cache.index.enable
>
> Keith
>
>
> On Mon, Mar 11, 2013 at 2:48 PM, Slater, David M.
> <David.Slater@jhuapl.edu> wrote:
>> Hi,
>>
>>
>>
>> I have a four-node setup, and I'm running some intensive query 
>> operations that need to go through all of the rows (though only one 
>> or two column families). While I don't expect this to be fast by any 
>> means, I wanted to make sure that I had a decent baseline before 
>> comparing this to more indexed versions of querying. Here is the
>> problem: Two of my nodes have very low data cache hit rates, wand I 
>> assume that this would greatly impact the query efficiency. Is this correct?
>>
>>
>>
>> All four of my nodes have a 99% index cache hit rate, but the data 
>> cache hit rates are:
>>
>> Node 1: 96%
>>
>> Node 2: 95%
>>
>> Node 3: 67%
>>
>> Node 4: 0%
>>
>> (All four are data nodes; the name node is #1)
>>
>>
>>
>> I'm not seeing any warnings or errors in the logs, and I couldn't 
>> find much online about it, so I thought I would check here. Does 
>> anyone have a suggestion as for how to fix it? Could this be related 
>> to the system swappiness at all? (I currently have swappiness set to 
>> 0.)
>>
>>
>>
>> Thanks for the help,
>> David Slater

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