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....@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 < dma...@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....@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 < dma...@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.scherbak...@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.goncha...@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....@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 < >> > > dsetrak...@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.goncha...@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 < >> > > maxmu...@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....@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 < >> > > > > > voze...@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.scherbak...@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
