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From Anton Vinogradov ...@apache.org>
Subject Re: Rebalancing - how to make it faster
Date Mon, 26 Mar 2018 15:20:32 GMT
+1 for IEP creation

2018-03-23 22:40 GMT+03:00 Dmitry Pavlov <dpavlov.spb@gmail.com>:

> Denis, as I understood, there is and idea to exclude only rebalanced
> partition(s) data. All other data will go to the WAL.
>
> Ilya, please correct me if I'm wrong.
>
> пт, 23 мар. 2018 г. в 22:15, Denis Magda <dmagda@apache.org>:
>
> > Ilya,
> >
> > That's a decent boost (5-20%) even having WAL enabled. Not sure that we
> > should stake on the WAL "off" mode here because if the whole cluster goes
> > down, it's then the data consistency is questionable. As an architect, I
> > wouldn't disable WAL for the sake of rebalancing; it's too risky.
> >
> > If you agree, then let's create the IEP. This way it will be easier to
> > track this endeavor. BTW, are you already ready to release any
> > optimizations in 2.5 that is being discussed in a separate thread?
> >
> > --
> > Denis
> >
> >
> >
> > On Fri, Mar 23, 2018 at 6:37 AM, Ilya Lantukh <ilantukh@gridgain.com>
> > wrote:
> >
> > > Denis,
> > >
> > > > - Don't you want to aggregate the tickets under an IEP?
> > > Yes, I think so.
> > >
> > > > - Does it mean we're going to update our B+Tree implementation? Any
> > ideas
> > > how risky it is?
> > > One of tickets that I created (
> > > https://issues.apache.org/jira/browse/IGNITE-7935) involves B+Tree
> > > modification, but I am not planning to do it in the nearest future. It
> > > shouldn't affect existing tree operations, only introduce new ones
> > (putAll,
> > > invokeAll, removeAll).
> > >
> > > > - Any chance you had a prototype that shows performance optimizations
> > the
> > > approach you are suggesting to take?
> > > I have a prototype for simplest improvements (
> https://issues.apache.org/
> > > jira/browse/IGNITE-8019 & https://issues.apache.org/
> > > jira/browse/IGNITE-8018)
> > > - together they increase throughput by 5-20%, depending on
> configuration
> > > and environment. Also, I've tested different WAL modes - switching from
> > > LOG_ONLY to NONE gives over 100% boost - this is what I expect from
> > > https://issues.apache.org/jira/browse/IGNITE-8017.
> > >
> > > On Thu, Mar 22, 2018 at 9:48 PM, Denis Magda <dmagda@apache.org>
> wrote:
> > >
> > > > Ilya,
> > > >
> > > > That's outstanding research and summary. Thanks for spending your
> time
> > on
> > > > this.
> > > >
> > > > Not sure I have enough expertise to challenge your approach, but it
> > > sounds
> > > > 100% reasonable to me. As side notes:
> > > >
> > > >    - Don't you want to aggregate the tickets under an IEP?
> > > >    - Does it mean we're going to update our B+Tree implementation?
> Any
> > > >    ideas how risky it is?
> > > >    - Any chance you had a prototype that shows performance
> > optimizations
> > > of
> > > >    the approach you are suggesting to take?
> > > >
> > > > --
> > > > Denis
> > > >
> > > > On Thu, Mar 22, 2018 at 8:38 AM, Ilya Lantukh <ilantukh@gridgain.com
> >
> > > > wrote:
> > > >
> > > > > Igniters,
> > > > >
> > > > > I've spent some time analyzing performance of rebalancing process.
> > The
> > > > > initial goal was to understand, what limits it's throughput,
> because
> > it
> > > > is
> > > > > significantly slower than network and storage device can
> > theoretically
> > > > > handle.
> > > > >
> > > > > Turns out, our current implementation has a number of issues caused
> > by
> > > a
> > > > > single fundamental problem.
> > > > >
> > > > > During rebalance data is sent in batches called
> > > > > GridDhtPartitionSupplyMessages. Batch size is configurable,
> default
> > > > value
> > > > > is 512KB, which could mean thousands of key-value pairs. However,
> we
> > > > don't
> > > > > take any advantage over this fact and process each entry
> > independently:
> > > > > - checkpointReadLock is acquired multiple times for every entry,
> > > leading
> > > > to
> > > > > unnecessary contention - this is clearly a bug;
> > > > > - for each entry we write (and fsync, if configuration assumes it)
> a
> > > > > separate WAL record - so, if batch contains N entries, we might end
> > up
> > > > > doing N fsyncs;
> > > > > - adding every entry into CacheDataStore also happens completely
> > > > > independently. It means, we will traverse and modify each index
> tree
> > N
> > > > > times, we will allocate space in FreeList N times and we will have
> to
> > > > > additionally store in WAL O(N*log(N)) page delta records.
> > > > >
> > > > > I've created a few tickets in JIRA with very different levels of
> > scale
> > > > and
> > > > > complexity.
> > > > >
> > > > > Ways to reduce impact of independent processing:
> > > > > - https://issues.apache.org/jira/browse/IGNITE-8019 -
> aforementioned
> > > > bug,
> > > > > causing contention on checkpointReadLock;
> > > > > - https://issues.apache.org/jira/browse/IGNITE-8018 - inefficiency
> > in
> > > > > GridCacheMapEntry implementation;
> > > > > - https://issues.apache.org/jira/browse/IGNITE-8017 -
> automatically
> > > > > disable
> > > > > WAL during preloading.
> > > > >
> > > > > Ways to solve problem on more global level:
> > > > > - https://issues.apache.org/jira/browse/IGNITE-7935 - a ticket to
> > > > > introduce
> > > > > batch modification;
> > > > > - https://issues.apache.org/jira/browse/IGNITE-8020 - complete
> > > redesign
> > > > of
> > > > > rebalancing process for persistent caches, based on file transfer.
> > > > >
> > > > > Everyone is welcome to criticize above ideas, suggest new ones or
> > > > > participate in implementation.
> > > > >
> > > > > --
> > > > > Best regards,
> > > > > Ilya
> > > > >
> > > >
> > >
> > >
> > >
> > > --
> > > Best regards,
> > > Ilya
> > >
> >
>

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