On Tue, Mar 12, 2013 at 11:46 AM, Slater, David M. <[email protected]> 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:[email protected]] > Sent: Monday, March 11, 2013 3:02 PM > To: [email protected] > 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. > <[email protected]> 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
