On Fri, Oct 21, 2016 at 1:41 AM, Ravikumar Govindarajan < [email protected]> wrote:
> Our application makes use of 'write-thru-block-cache' only. During > search/merge-reads, we have modified block-cache code to only probe the > block-cache and avoid inserting to it. > > In such a usage scenario, I was thinking about introducing a > 'readBufferSize' (default=1KB) in CacheIndexInput. From block-cache or > underlying file we read only 'readBufferSize' data & adjust counters > accordingly when it's a short-circuit read... > > You think it could be made workable? > Yeah it should be. > > Another idea could be to bypass the cache directory during merges and read > > directly from the hdfsdirectory. Then perhaps you could take advantage > of > > the SC reads without having to deal with the cache directly. > > > This is what we are currently evaluating & it looks to be a safe bet > Ok, let me know if you have any questions. > > -- > Ravi > > On Fri, Oct 21, 2016 at 3:26 AM, Aaron McCurry <[email protected]> wrote: > > > I my experience I too have used block cache sizes in the 64KB range for > the > > same reasons you listed. The biggest of which was because we were > running > > upwards of 100GB caches and 1K block cache sizes are not really possible > at > > that size. The biggest probably with the compaction is with the .tim > file, > > the rest of the files are mostly sequential reads, but because that file > is > > a tree it tends to jump all over the place during compaction. I would > > recommend if you want to speed up compaction (merges) to allow the tim > > files to be put into block cache during the merge (e.i. turn quiet reads > > off for those files). This of course could flow your cache with data > that > > you are about to remove, so if you have the cache space it's the easiest > > solution. > > > > Another idea could be to bypass the cache directory during merges and > read > > directly from the hdfsdirectory. Then perhaps you could take advantage > of > > the SC reads without having to deal with the cache directly. > > > > Aaron > > > > On Thu, Oct 20, 2016 at 3:53 AM, Ravikumar Govindarajan < > > [email protected]> wrote: > > > > > We have set a fairly large cacheSize of 64KB in block-cache for > avoiding > > > too many keys, gc pressure etc... > > > > > > But CacheIndexInput tries to read 64KB of data during a cache-miss & > > fills > > > up the CacheValue. When doing short-circuit-reads, this could turn out > to > > > be excessive no? For a comparison, lucene uses only 1KB buffers for the > > > same.. > > > > > > Do you think this will likely affect performance of searches albeit in > a > > > minor way? > > > > > > -- > > > Ravi > > > > > >
