ignite-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Maxim Muzafarov <maxmu...@gmail.com>
Subject ***UNCHECKED*** Re: Re[4]: Cache scan efficiency
Date Wed, 19 Sep 2018 09:15:42 GMT
Alexei,

> Summing up, I suggest adding new public
method IgniteCache.preloadPartition(partId).

If I understand correctly use case, the user wants to retrieve whole data
from
the cache (not only single partition) having slow HDD. So, my suggestion is
to
create methods of public API like these:

`public IgniteCache<K, V> withPartitionsWarmup();`
`public IgniteCache<K, V> withPartitionWarmup(int partition);`

On Wed, 19 Sep 2018 at 09:59 Zhenya Stanilovsky <arzamas123@mail.ru.invalid>
wrote:

> Great, i don`t think about that.
>
>
> >Среда, 19 сентября 2018, 9:40 +03:00 от Vladimir Ozerov <
> vozerov@gridgain.com>:
> >
> >Pinning is even worse thing, because you loose control on how data is
> moved
> >within a single region. Instead, I would suggest to use partition warmup +
> >separate data region to achieve "pinning" semantics.
> >
> >On Wed, Sep 19, 2018 at 8:34 AM Zhenya Stanilovsky
> >< arzamas123@mail.ru.invalid > wrote:
> >
> >> hi, but how to deal with page replacements, which Dmitriy Pavlov
> mentioned?
> >> this approach would be efficient if all data fits into memory, may be
> >> better to have method to pin some critical caches?
> >>
> >>
> >> >Среда, 19 сентября 2018, 0:26 +03:00 от Dmitriy Pavlov <
> >>  dpavlov.spb@gmail.com >:
> >> >
> >> >Even better, if RAM is exhausted page replacement process will be
> started.
> >> >
> >>
> https://cwiki.apache.org/confluence/display/IGNITE/Ignite+Durable+Memory+-+under+the+hood#IgniteDurableMemory-underthehood-Pagereplacement(rotationwithdisk
> >> )
> >> >
> >> >Effect of the preloading will be still markable, but not as excelled as
> >> >with full-fitting into RAM. Later I can review or improve javadocs if
> it
> >> is
> >> >necessary.
> >> >
> >> >ср, 19 сент. 2018 г. в 0:18, Denis Magda <  dmagda@apache.org
>:
> >> >
> >> >> Agree, it's just a matter of the documentation. If a user stores
> 100% in
> >> >> RAM and on disk, and just wants to warm RAM up after a restart then
> he
> >> >> knows everything will fit there. If during the preloading we detect
> that
> >> >> the RAM is exhausted we can halt it and print out a warning.
> >> >>
> >> >> --
> >> >> Denis
> >> >>
> >> >> On Tue, Sep 18, 2018 at 2:10 PM Dmitriy Pavlov <
> dpavlov.spb@gmail.com
> >> >
> >> >> wrote:
> >> >>
> >> >> > Hi,
> >> >> >
> >> >> > I totally support the idea of cache preload.
> >> >> >
> >> >> > IMO it can be expanded. We can iterate over local partitions of
the
> >> cache
> >> >> > group and preload each.
> >> >> >
> >> >> > But it should be really clear documented methods so a user can
be
> >> aware
> >> >> of
> >> >> > the benefits of such method (e.g. if RAM region is big enough,
> etc).
> >> >> >
> >> >> > Sincerely,
> >> >> > Dmitriy Pavlov
> >> >> >
> >> >> > вт, 18 сент. 2018 г. в 21:36, Denis Magda <  dmagda@apache.org
>:
> >> >> >
> >> >> > > Folks,
> >> >> > >
> >> >> > > Since we're adding a method that would preload a certain
> partition,
> >> can
> >> >> > we
> >> >> > > add the one which will preload the whole cache? Ignite
> persistence
> >> >> users
> >> >> > > I've been working with look puzzled once they realize there
is no
> >> way
> >> >> to
> >> >> > > warm up RAM after the restart. There are use cases that require
> >> this.
> >> >> > >
> >> >> > > Can the current optimizations be expanded to the cache preloading
> >> use
> >> >> > case?
> >> >> > >
> >> >> > > --
> >> >> > > Denis
> >> >> > >
> >> >> > > On Tue, Sep 18, 2018 at 3:58 AM Alexei Scherbakov <
> >> >> > >  alexey.scherbakoff@gmail.com > wrote:
> >> >> > >
> >> >> > > > Summing up, I suggest adding new public
> >> >> > > > method IgniteCache.preloadPartition(partId).
> >> >> > > >
> >> >> > > > I will start preparing PR for IGNITE-8873
> >> >> > > > <  https://issues.apache.org/jira/browse/IGNITE-8873
> if no
> more
> >> >> > > objections
> >> >> > > > follow.
> >> >> > > >
> >> >> > > >
> >> >> > > >
> >> >> > > > вт, 18 сент. 2018 г. в 10:50, Alexey Goncharuk
<
> >> >> > >  alexey.goncharuk@gmail.com
> >> >> > > > >:
> >> >> > > >
> >> >> > > > > Dmitriy,
> >> >> > > > >
> >> >> > > > > In my understanding, the proper fix for the scan
query looks
> >> like a
> >> >> > big
> >> >> > > > > change and it is unlikely that we include it in
Ignite 2.7.
> On
> >> the
> >> >> > > other
> >> >> > > > > hand, the method suggested by Alexei is quite simple
 and it
> >> >> > definitely
> >> >> > > > > fits Ignite 2.7, which will provide a better user
experience.
> >> Even
> >> >> > > > having a
> >> >> > > > > proper scan query implemented this method can be
useful in
> some
> >> >> > > specific
> >> >> > > > > scenarios, so we will not have to deprecate it.
> >> >> > > > >
> >> >> > > > > --AG
> >> >> > > > >
> >> >> > > > > пн, 17 сент. 2018 г. в 19:15, Dmitriy Pavlov
<
> >> >>  dpavlov.spb@gmail.com
> >> >> > >:
> >> >> > > > >
> >> >> > > > > > As I understood it is not a hack, it is an
advanced feature
> >> for
> >> >> > > warming
> >> >> > > > > up
> >> >> > > > > > the partition. We can build warm-up of the
overall cache by
> >> >> calling
> >> >> > > its
> >> >> > > > > > partitions warm-up. Users often ask about
this feature and
> are
> >> >> not
> >> >> > > > > > confident with our lazy upload.
> >> >> > > > > >
> >> >> > > > > > Please correct me if I misunderstood the idea.
> >> >> > > > > >
> >> >> > > > > > пн, 17 сент. 2018 г. в 18:37, Dmitriy
Setrakyan <
> >> >> > >  dsetrakyan@apache.org
> >> >> > > > >:
> >> >> > > > > >
> >> >> > > > > > > I would rather fix the scan than hack
the scan. Is there
> any
> >> >> > > > technical
> >> >> > > > > > > reason for hacking it now instead of
fixing it properly?
> Can
> >> >> some
> >> >> > > of
> >> >> > > > > the
> >> >> > > > > > > experts in this thread provide an estimate
of complexity
> and
> >> >> > > > difference
> >> >> > > > > > in
> >> >> > > > > > > work that would be required for each
approach?
> >> >> > > > > > >
> >> >> > > > > > > D.
> >> >> > > > > > >
> >> >> > > > > > > On Mon, Sep 17, 2018 at 4:42 PM Alexey
Goncharuk <
> >> >> > > > > > >  alexey.goncharuk@gmail.com >
> >> >> > > > > > > wrote:
> >> >> > > > > > >
> >> >> > > > > > > > I think it would be beneficial for
some Ignite users
> if we
> >> >> > added
> >> >> > > > > such a
> >> >> > > > > > > > partition warmup method to the public
API. The method
> >> should
> >> >> be
> >> >> > > > > > > > well-documented and state that it
may invalidate
> existing
> >> >> page
> >> >> > > > cache.
> >> >> > > > > > It
> >> >> > > > > > > > will be a very effective instrument
until we add the
> >> proper
> >> >> > scan
> >> >> > > > > > ability
> >> >> > > > > > > > that Vladimir was referring to.
> >> >> > > > > > > >
> >> >> > > > > > > > пн, 17 сент. 2018 г. в 13:05,
Maxim Muzafarov <
> >> >> > >  maxmuzaf@gmail.com
> >> >> > > > >:
> >> >> > > > > > > >
> >> >> > > > > > > > > Folks,
> >> >> > > > > > > > >
> >> >> > > > > > > > > Such warming up can be an effective
technique for
> >> >> performing
> >> >> > > > > > > calculations
> >> >> > > > > > > > > which required large cache
> >> >> > > > > > > > > data reads, but I think it's
the single narrow use
> case
> >> of
> >> >> > all
> >> >> > > > over
> >> >> > > > > > > > Ignite
> >> >> > > > > > > > > store usages. Like all other
> >> >> > > > > > > > > powerfull techniques, we should
use it wisely. In the
> >> >> general
> >> >> > > > > case, I
> >> >> > > > > > > > think
> >> >> > > > > > > > > we should consider other
> >> >> > > > > > > > > techniques mentioned by Vladimir
and may create
> >> something
> >> >> > like
> >> >> > > > > > `global
> >> >> > > > > > > > > statistics of cache data usage`
> >> >> > > > > > > > > to choose the best technique
in each case.
> >> >> > > > > > > > >
> >> >> > > > > > > > > For instance, it's not obvious
what would take
> longer:
> >> >> > > > multi-block
> >> >> > > > > > > reads
> >> >> > > > > > > > or
> >> >> > > > > > > > > 50 single-block reads issues
> >> >> > > > > > > > > sequentially. It strongly depends
on used hardware
> under
> >> >> the
> >> >> > > hood
> >> >> > > > > and
> >> >> > > > > > > > might
> >> >> > > > > > > > > depend on workload system
> >> >> > > > > > > > > resources (CPU-intensive calculations
and I\O
> access) as
> >> >> > well.
> >> >> > > > But
> >> >> > > > > > > > > `statistics` will help us to
choose
> >> >> > > > > > > > > the right way.
> >> >> > > > > > > > >
> >> >> > > > > > > > >
> >> >> > > > > > > > > On Sun, 16 Sep 2018 at 23:59
Dmitriy Pavlov <
> >> >> > > >  dpavlov.spb@gmail.com
> >> >> > > > > >
> >> >> > > > > > > > wrote:
> >> >> > > > > > > > >
> >> >> > > > > > > > > > Hi Alexei,
> >> >> > > > > > > > > >
> >> >> > > > > > > > > > I did not find any PRs
associated with the ticket
> for
> >> >> check
> >> >> > > > code
> >> >> > > > > > > > changes
> >> >> > > > > > > > > > behind this idea. Are
there any PRs?
> >> >> > > > > > > > > >
> >> >> > > > > > > > > > If we create some forwards
scan of pages, it should
> >> be a
> >> >> > very
> >> >> > > > > > > > > intellectual
> >> >> > > > > > > > > > algorithm including a
lot of parameters (how much
> RAM
> >> is
> >> >> > > free,
> >> >> > > > > how
> >> >> > > > > > > > > probably
> >> >> > > > > > > > > > we will need next page,
etc). We had the private
> talk
> >> >> about
> >> >> > > > such
> >> >> > > > > > idea
> >> >> > > > > > > > > some
> >> >> > > > > > > > > > time ago.
> >> >> > > > > > > > > >
> >> >> > > > > > > > > > By my experience, Linux
systems already do such
> >> forward
> >> >> > > reading
> >> >> > > > > of
> >> >> > > > > > > file
> >> >> > > > > > > > > > data (for corresponding
sequential flagged file
> >> >> > descriptors),
> >> >> > > > but
> >> >> > > > > > > some
> >> >> > > > > > > > > > prefetching of data at
the level of application
> may be
> >> >> > useful
> >> >> > > > for
> >> >> > > > > > > > > O_DIRECT
> >> >> > > > > > > > > > file descriptors.
> >> >> > > > > > > > > >
> >> >> > > > > > > > > > And one more concern from
me is about selecting a
> >> right
> >> >> > place
> >> >> > > > in
> >> >> > > > > > the
> >> >> > > > > > > > > system
> >> >> > > > > > > > > > to do such prefetch.
> >> >> > > > > > > > > >
> >> >> > > > > > > > > > Sincerely,
> >> >> > > > > > > > > > Dmitriy Pavlov
> >> >> > > > > > > > > >
> >> >> > > > > > > > > > вс, 16 сент. 2018
г. в 19:54, Vladimir Ozerov <
> >> >> > > > > >  vozerov@gridgain.com
> >> >> > > > > > > >:
> >> >> > > > > > > > > >
> >> >> > > > > > > > > > > HI Alex,
> >> >> > > > > > > > > > >
> >> >> > > > > > > > > > > This is good that
you observed speedup. But I do
> not
> >> >> > think
> >> >> > > > this
> >> >> > > > > > > > > solution
> >> >> > > > > > > > > > > works for the product
in general case. Amount of
> >> RAM is
> >> >> > > > > limited,
> >> >> > > > > > > and
> >> >> > > > > > > > > > even a
> >> >> > > > > > > > > > > single partition
may need more space than RAM
> >> >> available.
> >> >> > > > > Moving a
> >> >> > > > > > > lot
> >> >> > > > > > > > > of
> >> >> > > > > > > > > > > pages to page memory
for scan means that you
> evict a
> >> >> lot
> >> >> > of
> >> >> > > > > other
> >> >> > > > > > > > > pages,
> >> >> > > > > > > > > > > what will ultimately
lead to bad performance of
> >> >> > subsequent
> >> >> > > > > > queries
> >> >> > > > > > > > and
> >> >> > > > > > > > > > > defeat LRU algorithms,
which are of great
> improtance
> >> >> for
> >> >> > > good
> >> >> > > > > > > > database
> >> >> > > > > > > > > > > performance.
> >> >> > > > > > > > > > >
> >> >> > > > > > > > > > > Database vendors
choose another approach - skip
> >> BTrees,
> >> >> > > > iterate
> >> >> > > > > > > > > direclty
> >> >> > > > > > > > > > > over data pages,
read them in multi-block
> fashion,
> >> use
> >> >> > > > separate
> >> >> > > > > > > scan
> >> >> > > > > > > > > > buffer
> >> >> > > > > > > > > > > to avoid excessive
evictions of other hot pages.
> >> >> > > > Corresponding
> >> >> > > > > > > ticket
> >> >> > > > > > > > > for
> >> >> > > > > > > > > > > SQL exists [1], but
idea is common for all parts
> of
> >> the
> >> >> > > > system,
> >> >> > > > > > > > > requiring
> >> >> > > > > > > > > > > scans.
> >> >> > > > > > > > > > >
> >> >> > > > > > > > > > > As far as proposed
solution, it might be good
> idea
> >> to
> >> >> add
> >> >> > > > > special
> >> >> > > > > > > API
> >> >> > > > > > > > > to
> >> >> > > > > > > > > > > "warmup" partition
with clear explanation of pros
> >> (fast
> >> >> > > scan
> >> >> > > > > > after
> >> >> > > > > > > > > > warmup)
> >> >> > > > > > > > > > > and cons (slowdown
of any other operations). But
> I
> >> >> think
> >> >> > we
> >> >> > > > > > should
> >> >> > > > > > > > not
> >> >> > > > > > > > > > make
> >> >> > > > > > > > > > > this approach part
of normal scans.
> >> >> > > > > > > > > > >
> >> >> > > > > > > > > > > Vladimir.
> >> >> > > > > > > > > > >
> >> >> > > > > > > > > > > [1]
> >>  https://issues.apache.org/jira/browse/IGNITE-6057
> >> >> > > > > > > > > > >
> >> >> > > > > > > > > > >
> >> >> > > > > > > > > > > On Sun, Sep 16, 2018
at 6:44 PM Alexei
> Scherbakov <
> >> >> > > > > > > > > > >  alexey.scherbakoff@gmail.com
> wrote:
> >> >> > > > > > > > > > >
> >> >> > > > > > > > > > > > Igniters,
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > > > My use case
involves scenario where it's
> >> necessary to
> >> >> > > > iterate
> >> >> > > > > > > over
> >> >> > > > > > > > > > > > large(many TBs)
persistent cache doing some
> >> >> calculation
> >> >> > > on
> >> >> > > > > read
> >> >> > > > > > > > data.
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > > > The basic solution
is to iterate cache using
> >> >> ScanQuery.
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > > > This turns out
to be slow because iteration
> over
> >> >> cache
> >> >> > > > > > involves a
> >> >> > > > > > > > lot
> >> >> > > > > > > > > > of
> >> >> > > > > > > > > > > > random disk
access for reading data pages
> >> referenced
> >> >> > from
> >> >> > > > > leaf
> >> >> > > > > > > > pages
> >> >> > > > > > > > > by
> >> >> > > > > > > > > > > > links.
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > > > This is especially
true when data is stored on
> >> disks
> >> >> > with
> >> >> > > > > slow
> >> >> > > > > > > > random
> >> >> > > > > > > > > > > > access, like
SAS disks. In my case on modern
> SAS
> >> >> disks
> >> >> > > > array
> >> >> > > > > > > > reading
> >> >> > > > > > > > > > > speed
> >> >> > > > > > > > > > > > was like several
MB/sec while sequential read
> >> speed
> >> >> in
> >> >> > > perf
> >> >> > > > > > test
> >> >> > > > > > > > was
> >> >> > > > > > > > > > > about
> >> >> > > > > > > > > > > > GB/sec.
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > > > I was able to
fix the issue by using ScanQuery
> >> with
> >> >> > > > explicit
> >> >> > > > > > > > > partition
> >> >> > > > > > > > > > > set
> >> >> > > > > > > > > > > > and running
simple warmup code before each
> >> partition
> >> >> > > scan.
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > > > The code pins
cold pages in memory in
> sequential
> >> >> order
> >> >> > > thus
> >> >> > > > > > > > > eliminating
> >> >> > > > > > > > > > > > random disk
access. Speedup was like x100
> >> magnitude.
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > > > I suggest adding
the improvement to the
> product's
> >> >> core
> >> >> > > by
> >> >> > > > > > always
> >> >> > > > > > > > > > > > sequentially
preloading pages for all internal
> >> >> > partition
> >> >> > > > > > > iterations
> >> >> > > > > > > > > > > (cache
> >> >> > > > > > > > > > > > iterators, scan
queries, sql queries with scan
> >> plan)
> >> >> if
> >> >> > > > > > partition
> >> >> > > > > > > > is
> >> >> > > > > > > > > > cold
> >> >> > > > > > > > > > > > (low number
of pinned pages).
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > > > This also should
speed up rebalancing from cold
> >> >> > > partitions.
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > > > Ignite JIRA
ticket [1]
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > > > Thoughts ?
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > > > [1]
> >> >>  https://issues.apache.org/jira/browse/IGNITE-8873
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > > > --
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > > > Best regards,
> >> >> > > > > > > > > > > > Alexei Scherbakov
> >> >> > > > > > > > > > > >
> >> >> > > > > > > > > > >
> >> >> > > > > > > > > >
> >> >> > > > > > > > > --
> >> >> > > > > > > > > --
> >> >> > > > > > > > > Maxim Muzafarov
> >> >> > > > > > > > >
> >> >> > > > > > > >
> >> >> > > > > > >
> >> >> > > > > >
> >> >> > > > >
> >> >> > > >
> >> >> > > >
> >> >> > > > --
> >> >> > > >
> >> >> > > > Best regards,
> >> >> > > > Alexei Scherbakov
> >> >> > > >
> >> >> > >
> >> >> >
> >> >>
> >>
> >>
> >> --
> >> Zhenya Stanilovsky
> >>
>
>
> --
> Zhenya Stanilovsky
>
-- 
--
Maxim Muzafarov

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message