One possible explanation is that the OS's native file system caching is
being successful at keeping these files mostly in RAM most of the time.
And so the performance benefits of 'forcing' the files into RAM by
using tmpfs aren't significant.
So the slowness of the queries is the result of being CPU bound, rather
than IO bound. The cache within Solr is faster because it is saving and
returning the information for which the CPU-bound work has already been
done.
Just one possible explanation.
Sean Fox
Matthew Phillips wrote:
No one has a suggestion? I must be missing something because as I
understand it from Dennis' email, all of queries are very quick (cached
type response times) whereas mine are not. I can clearly see time
differences between queries that are cached (things that have been auto
warmed) and queries that are not. This seems odd as my whole index is
loaded on a tmpfs memory based file system. Thanks for the help.
Matt
On Dec 4, 2007, at 3:55 PM, Matthew Phillips wrote:
Thanks for the suggestion, Dennis. I decided to implement this as you
described on my collection of about 400,000 documents, but I did not
receive the results I expected.
Prior to putting the indexes on a tmpfs, I did a bit of benchmarking
and found that it usually takes a little under two seconds for each
facet query. After moving my indexes from disk to a tmpfs file system,
I seem to get about the same result from facet queries: about two
seconds.
Does anyone have any insight into this? Doesn't it seem odd that my
response times are about the same? Thanks for the help.
Matt Phillips
Dennis Kubes wrote:
One way to do this if you are running on linux is to create a tempfs
(which is ram) and then mount the filesystem in the ram. Then your
index acts normally to the application but is essentially served from
Ram. This is how we server the Nutch lucene indexes on our web
search engine (www.visvo.com) which is ~100M pages. Below is how you
can achieve this, assuming your indexes are in /path/to/indexes:
mv /path/to/indexes /path/to/indexes.dist
mkdir /path/to/indexes
cd /path/to
mount -t tmpfs -o size=2684354560 none /path/to/indexes
rsync --progress -aptv indexes.dist/* indexes/
chown -R user:group indexes
This would of course be limited by the amount of RAM you have on the
machine. But with this approach most searches are sub-second.
Dennis Kubes
Evgeniy Strokin wrote:
Hello,...
we have 110M records index under Solr. Some queries takes a while,
but we need sub-second results. I guess the only solution is cache
(something else?)...
We use standard LRUCache. In docs it says (as far as I understood)
that it loads view of index in to memory and next time works with
memory instead of hard drive.
So, my question: hypothetically, we can have all index in memory if
we'd have enough memory size, right? In this case the result should
come up very fast. We have very rear updates. So I think this could
be a solution.
How should I configure the cache to achieve such approach?
Thanks for any advise.
Gene
