From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 6 Feb 2019 20:04:23 +0300 From: Vladimir Davydov Subject: Re: [tarantool-patches] Re: [PATCH 6/9] vinyl: set range size automatically Message-ID: <20190206170423.4dv7slwyecuubdqt@esperanza> References: <6cd378d1640f87d46a6e40f1c51e4ae62a70c209.1548017258.git.vdavydov.dev@gmail.com> <20190205170909.GE6811@chai> <20190206092331.tpqfx2odv45fqqlx@esperanza> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190206092331.tpqfx2odv45fqqlx@esperanza> To: Konstantin Osipov Cc: tarantool-patches@freelists.org List-ID: On Wed, Feb 06, 2019 at 12:23:31PM +0300, Vladimir Davydov wrote: > On Tue, Feb 05, 2019 at 08:09:09PM +0300, Konstantin Osipov wrote: > > * Vladimir Davydov [19/01/21 06:58]: > > > +int64_t > > > +vy_lsm_range_size(struct vy_lsm *lsm) > > > +{ > > > + /* Use the configured range size if available. */ > > > + if (lsm->opts.range_size > 0) > > > + return lsm->opts.range_size; > > > + /* > > > + * It doesn't make much sense to create too small ranges. > > > + * Limit the max number of ranges per index to 1000 and > > > + * never create ranges smaller than 16 MB. > > > + */ > > > + enum { MIN_RANGE_SIZE = 16 * 1024 * 1024 }; > > > + enum { MAX_RANGE_COUNT = 1000 }; > > > + /* > > > + * Ideally, we want to compact roughly the same amount of > > > + * data after each dump so as to avoid IO bursts caused by > > > + * simultaneous major compaction of a bunch of ranges, > > > + * because such IO bursts can lead to a deviation of the > > > + * LSM tree from the configured shape and, as a result, > > > + * increased read amplification. To achieve that, we need > > > + * to have at least as many ranges as the number of dumps > > > + * it takes to trigger major compaction in a range. > > > + */ > > > + int range_count = vy_lsm_dumps_per_compaction(lsm); > > > + range_count = MIN(range_count, MAX_RANGE_COUNT); > > > + int64_t range_size = lsm->stat.disk.last_level_count.bytes / > > > + (range_count + 1); > > > + range_size = MAX(range_size, MIN_RANGE_SIZE); > > > + return range_size; > > > +} > > > > OK, you could say the value is rarely used, so can be calculated > > each time it is used, but why instead not recalculate it on each > > major compaction? This would spare us from technical debt and > > having to think about potential performance bottleneck in the > > future. > > Well, okay, I think we can do that, too. Come to think of it, I'd prefer not to, because this would one more member to struct vy_lsm, which we would have to update on dump and compaction - it's more error prone IMO. Since calculation of the target range size is trivial and called rarely (on split/coalesce), I think we should leave it as is.