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From Fay Hou [Storage Service] ­ <fay...@coupang.com>
Subject Re: index_interval
Date Wed, 12 Jul 2017 19:03:59 GMT
First, a big thank to Jeff who spent endless time to help this mailing list.
Agreed that we should tune the key cache. In my case, my key cache hit rate
is about 20%. mainly because we do random read. We just going to leave the
index_interval as is for now.

On Mon, Jul 10, 2017 at 8:47 PM, Jeff Jirsa <jjirsa@apache.org> wrote:

>
>
> On 2017-07-10 15:09 (-0700), Fay Hou [Storage Service] ­ <
> fayhou@coupang.com> wrote:
> > BY defaults:
> >
> > AND max_index_interval = 2048
> >     AND memtable_flush_period_in_ms = 0
> >     AND min_index_interval = 128
> >
> > "Cassandra maintains index offsets per partition to speed up the lookup
> > process in the case of key cache misses (see cassandra read path overview
> > <http://docs.datastax.com/en/cassandra/2.1/cassandra/dml/
> dml_about_reads_c.html>).
> > By default it samples a subset of keys, somewhat similar to a skip list.
> > The sampling interval is configurable with min_index_interval and
> > max_index_interval CQL schema attributes (see describe table). For
> > relatively large blobs like HTML pages we seem to get better read
> latencies
> > by lowering the sampling interval from 128 min / 2048 max to 64 min / 512
> > max. For large tables like parsoid HTML with ~500G load per node this
> > change adds a modest ~25mb off-heap memory."
> >
> > I wonder if any one has experience on working with max and min
> index_interval
> > to increase the read speed.
>
> It's usually more efficient to try to tune the key cache, and hope you
> never have to hit the partition index at all. Do you have reason to believe
> you're spending an inordinate amount of IO scanning the partition index? Do
> you know what your key cache hit rate is?
>
>
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