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From Matt <dromitl...@gmail.com>
Subject Re: CacheStore's Performance Drops Dramatically - Why?
Date Wed, 03 May 2017 06:26:21 GMT
I'm writing to confirm I managed to fix my problem by fine tuning the
config params for the write behind cache until the performance was fine. I
still see single element inserts from time to time, but just a few of them
every now and then not like before. You should definitely avoid synchronous
single elements insertions, I hope that changes in future versions.

Regarding writeBehindBatchSize and writeBehindFlushSize, I don't see the
point of setting both values when batchSize < flushSize (default values are
512 and 10240 respectively). If I'm not wrong, the cache is flushed
whenever the its size is equal to min(batchSize, flushSize). Since
batchSize is less than flushSize, flushSize is never really used and the
size of the flush is controlled by the size of the cache itself only.

That is how it works by default, on the other hand if we swap their values
(ie, batchSize=10240 and flushSize=512) the behavior would be the same
(Ignite would call writeAll() with 512 elements each time), but the number
of elements flushed would be controlled by the correct variable (ie,
flushSize).

Were the default values supposed to be the other way around or am I missing
something?

On Tue, May 2, 2017 at 9:13 PM, Denis Magda <dmagda@apache.org> wrote:

> Matt,
>
> Cross-posting to the dev list.
>
> Yes, Ignite switches to the synchronous mode once the buffer is exhausted.
> However, I do agree that it would be a right solution to flush multiple
> entries rather than one in the synchronous mode. *Igniters*, I was sure we
> had a ticket for that optimization but unable to find it.  Does anybody
> know the ticket name/number?
>
> To omit the performance degradation you have to tweak the following
> parameters so that the write-behind store can keep up with you updates:
> - setWriteBehindFlushThreadCount
> - setWriteBehindFlushFrequency
> - setWriteBehindBatchSize
> - setWriteBehindFlushSize
>
> Usually it helped all the times to Apache Ignite users.
>
> > QUESTION 2
> >
> > I've read on the docs that using ATOMIC mode (default mode) is better
> for performance, but I'm not getting why. If I'm not wrong using
> TRANSACTIONAL mode would cause the CacheStore to reuse connections (not
> call openConnection(autocommit=true) on each writeAll()).
> >
> > Shouldn't it be better to use transactional mode?
>
> Transactional mode enables 2 phase commit protocol:
> https://apacheignite.readme.io/docs/transactions#two-phase-commit-2pc
>
> This is why atomic operations are swifter in general.
>
> —
> Denis
>
> > On May 2, 2017, at 10:40 AM, Matt <dromitlabs@gmail.com> wrote:
> >
> > No, only with inserts, I haven't tried removing at this rate yet but it
> may have the same problem.
> >
> > I'm debugging Ignite internal code and I may be onto something. The
> thing is Ignite has a cacheMaxSize (aka, WriteBehindFlushSize) and
> cacheCriticalSize (which by default is cacheMaxSize*1.5). When the cache
> reaches that size Ignite starts writing elements SYNCHRONOUSLY, as you can
> see in [1].
> >
> > I think this makes things worse since only one single value is flushed
> at a time, it becomes much slower forcing Ignite to do more synchronous
> writes.
> >
> > Anyway, I'm still not sure why the cache reaches that level when the
> database is clearly able to keep up with the insertions. I'll check if it
> has to do with the number of open connections or what.
> >
> > Any insight on this is very welcome!
> >
> > [1] https://github.com/apache/ignite/blob/master/modules/
> core/src/main/java/org/apache/ignite/internal/processors/cache/store/
> GridCacheWriteBehindStore.java#L620
> >
> > On Tue, May 2, 2017 at 2:17 PM, Jessie Lin <jessie.jianwei.lin@gmail.com>
> wrote:
> > I noticed that behavior when any cache.remove operation is involved. I
> keep putting stuff in cache seems to be working properly.
> >
> > Do you use remove operation?
> >
> > On Tue, May 2, 2017 at 9:57 AM, Matt <dromitlabs@gmail.com> wrote:
> > I'm stuck with that. No matter what config I use (flush size, write
> threads, etc) this is the behavior I always get. It's as if Ignite internal
> buffer is full and it's trying to write and get rid of the oldest (one)
> element only.
> >
> > Any idea people? What is your CacheStore configuration to avoid this?
> >
> > On Tue, May 2, 2017 at 11:50 AM, Jessie Lin <
> jessie.jianwei.lin@gmail.com> wrote:
> > Hello Matt, thank you for posting. I've noticed similar behavior.
> >
> > Would be curious to see the response from the engineering team.
> >
> > Best,
> > Jessie
> >
> > On Tue, May 2, 2017 at 1:03 AM, Matt <dromitlabs@gmail.com> wrote:
> > Hi all,
> >
> > I have two questions for you!
> >
> > QUESTION 1
> >
> > I'm following the example in [1] (a mix between "jdbc transactional" and
> "jdbc bulk operations") and I've enabled write behind, however after the
> first 10k-20k insertions the performance drops *dramatically*.
> >
> > Based on prints I've added to the CacheStore, I've noticed what Ignite
> is doing is this:
> >
> > - writeAll called with 512 elements (Ignites buffers elements, that's
> good)
> > - openConnection with autocommit=true is called each time inside
> writeAll (since session is not stored in atomic mode)
> > - writeAll is called with 512 elements a few dozen times, each time it
> opens a new JDBC connection as mentioned above
> > - ...
> > - writeAll called with ONE element (for some reason Ignite stops
> buffering elements)
> > - writeAll is called with ONE element from here on, each time it opens a
> new JDBC connection as mentioned above
> > - ...
> >
> > Things to note:
> >
> > - All config values are the defaults ones except for write through and
> write behind which are both enabled.
> > - I'm running this as a server node (only one node on the cluster, the
> application itself).
> > - I see the problem even with a big heap (ie, Ignite is not nearly out
> of memory).
> > - I'm using PostgreSQL for this test (it's fine ingesting around 40k
> rows per second on this computer, so that shouldn't be a problem)
> >
> > What is causing Ignite to stop buffering elements after calling
> writeAll() a few dozen times?
> >
> > QUESTION 2
> >
> > I've read on the docs that using ATOMIC mode (default mode) is better
> for performance, but I'm not getting why. If I'm not wrong using
> TRANSACTIONAL mode would cause the CacheStore to reuse connections (not
> call openConnection(autocommit=true) on each writeAll()).
> >
> > Shouldn't it be better to use transactional mode?
> >
> > Regards,
> > Matt
> >
> > [1] https://apacheignite.readme.io/docs/persistent-store#
> section-cachestore-example
> >
> >
> >
> >
>
>

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