Let me also say that I can still rerun the experiments for the (hopefully subsequent) camera-ready version if the problem takes longer to fix.
Cheers, Ingo > -----Original Message----- > From: Müller Ingo <[email protected]> > Sent: Tuesday, August 10, 2021 5:34 PM > To: [email protected] > Subject: RE: Increasing degree of parallelism when reading Parquet files > > Hey Mike! > > Thanks for confirming! I am happy to test any fixes that you may come up with. > If the happens to be simple and is fixed before Friday, I can still include > it in the > revision I am currently working on ;) Otherwise, it'd be great to be able to > mention a Jira issue or similar (maybe this mailing list thread is enough?) > that I > can refer to. > > Cheers, > Ingo > > > > -----Original Message----- > > From: Michael Carey <[email protected]> > > Sent: Tuesday, August 10, 2021 4:36 PM > > To: [email protected] > > Subject: Re: Increasing degree of parallelism when reading Parquet > > files > > > > Ingo, > > > > Got it! It sounds like we indeed have a parallelism performance bug > > in the area of threading for S3, then. Weird! We'll look into it... > > > > > > Cheers, > > > > Mike > > > > > > On 8/9/21 11:21 PM, Müller Ingo wrote: > > > > > > Hey Mike, > > > > Just to clarify: "partitions" is the same thing as I/O devices, > > right? I have configured 48 of those via "[nc]\niodevices=..." and see > > the corresponding folders with content show up on the file system. > > When I vary the number of these devices, I see that all other storage > > format change the degree of parallelism with my queries. That > > mechanism thus seems to work in general. It just doesn't seem to work > > for Parquet on S3. (I am not 100% sure if I tried other file formats > > on S3.) > > > > I have also tried to set compiler.parallelism to 4 for Parquet files > > on HDFS with a file:// path and did not see any effect, i.e., it used > > 48 threads, which corresponds to the number of I/O devices. However, > > with what Dmitry said, I guess that this is expected behavior and the > > flag should only influence the degree of parallelism after exchanges (which > > I > don't have in my queries). > > > > Cheers, > > Ingo > > > > > > > > -----Original Message----- > > From: Michael Carey <[email protected]> > > <mailto:[email protected]> > > Sent: Monday, August 9, 2021 10:10 PM > > To: [email protected] > > <mailto:[email protected]> > > Subject: Re: Increasing degree of parallelism when reading > Parquet > > files > > > > Ingo, > > > > Q: In your Parquet/S3 testing, what does your current cluster > > configuration look > > like? (I.e., how many partitions have you configured it with - > > physical storage > > partitions that is?) Even though your S3 data isn't stored > > inside > > AsterixDB in this > > case, the system still uses that info to decide how many > > parallel > > threads to use > > at the base of its query plans. (Obviously there is room for > > improvement on that > > behavior for use cases involving external storage. :-)) > > > > > > Cheers, > > > > Mike > > > > > > On 8/9/21 12:28 PM, Müller Ingo wrote: > > > > > > Hi Dmitry, > > > > Thanks a lot for checking! Indeed, my queries do not > have an > > exchange. > > However, the number of I/O devices has indeed worked well in > many > > cases: > > when I tried the various VM instance sizes, I always created as > many > > I/O devices > > as there were physical cores (i.e., half the number of logical > > CPUs). For internal > > storage as well as HDFS (both using the hdfs:// and the file:// > > protocol), I saw > > the full system being utilized. However, just for the case of > > Parquet on S3, I > > cannot seem to make it use more than 16 cores. > > > > Cheers, > > Ingo > > > > > > > > -----Original Message----- > > From: Dmitry Lychagin > > <[email protected]> > <mailto:[email protected]> > > <mailto:[email protected]> > > <mailto:[email protected]> > > Sent: Monday, August 9, 2021 9:10 PM > > To: [email protected] > > <mailto:[email protected]> > > <mailto:[email protected]> > > <mailto:[email protected]> > > Subject: Re: Increasing degree of parallelism > when reading > > Parquet files > > > > Hi Ingo, > > > > I checked the code and it seems that when > scanning external > > datasource we're > > using the same number of cores as there are > configured storage > > partitions (I/O > > devices). > > Therefore, if you want 96 cores to be used > when scanning > > Parquet files then you > > need to configure 96 I/O devices. > > > > Compiler.parallelism setting is supposed to > affect how many > > cores we use after > > the first EXCHANGE operator. However, if your > query doesn't > > have any > > EXCHANGEs then it'll use the number of cores > assigned for the > > initial data scan > > operator (number of I/O devices) > > > > Thanks, > > -- Dmitry > > > > > > On 8/9/21, 11:42 AM, "Müller Ingo" > > <[email protected]> <mailto:[email protected]> > > <mailto:[email protected]> <mailto:[email protected]> wrote: > > > > EXTERNAL EMAIL: Use caution when > opening attachments > > or clicking on links > > > > > > > > > > > > Dear Dmitry, > > > > Thanks a lot for the quick reply! I had not > though of this. > > However, I have tried > > out both ways just now (per query and in the > cluster > > configuration) and did not > > see any changes. Is there any way I can control > that the setting > > was applied > > successfully? I have also tried setting > compiler.parallelism to 4 > > and still observed > > 16 cores being utilized. > > > > Note that the observed degree of parallelism > does not > > correspond to anything > > related to the data set (I tried with every > > power > of two files > > between 1 and 128) > > or the cluster (I tried with every power of two > cores between 2 > > and 64, as well > > as 48 and 96) and I always see 16 cores being > used (or fewer, if > > the system has > > fewer). To me, this makes it unlikely that the > system really uses > > the semantics > > for p=0 or p<0, but looks more like some hard- > coded value. > > > > Cheers, > > Ingo > > > > > > > -----Original Message----- > > > From: Dmitry Lychagin > > <[email protected]> > <mailto:[email protected]> > > <mailto:[email protected]> > > <mailto:[email protected]> > > > Sent: Monday, August 9, 2021 7:25 PM > > > To: [email protected] > > <mailto:[email protected]> > > <mailto:[email protected]> > > <mailto:[email protected]> > > > Subject: Re: Increasing degree of > parallelism when reading > > Parquet files > > > > > > Ingo, > > > > > > > > > > > > We have `compiler.parallelism` parameter > that controls > > how many cores are > > > used for query execution. > > > > > > See > > > > > > > > > https://ci.apache.org/projects/asterixdb/sqlpp/manual.html#Parallelism > > _param > > > eter > > > > > > > > > <https://ci.apache.org/projects/asterixdb/sqlpp/manual.html#Parallelis > > m_para > > > > > > <https://ci.apache.org/projects/asterixdb/sqlpp/manual.html#Parallelism_para> > > > > <https://ci.apache.org/projects/asterixdb/sqlpp/manual.html#Parallelis > > m_para> > > > <https://ci.apache.org/projects/asterixdb/sqlpp/manual.html#Parallelism_para> > > meter> > > > > > > You can either set it per query (e.g. SET > > `compiler.parallelism` "-1";) , > > > > > > or globally in the cluster configuration: > > > > > > > > > > https://github.com/apache/asterixdb/blob/master/asterixdb/asterix- > > > app/src/main/resources/cc2.conf#L57 > > > > > > > > > > > > Thanks, > > > > > > -- Dmitry > > > > > > > > > > > > > > > > > > From: Müller Ingo > > <[email protected]> <mailto:[email protected]> > > <mailto:[email protected]> > > <mailto:[email protected]> > > > Reply-To: "[email protected]" > > <mailto:[email protected]> > > <mailto:[email protected]> > > <mailto:[email protected]> <[email protected]> > > <mailto:[email protected]> > > <mailto:[email protected]> > > <mailto:[email protected]> > > > Date: Monday, August 9, 2021 at 10:05 AM > > > To: "[email protected]" > > <mailto:[email protected]> > > <mailto:[email protected]> > > <mailto:[email protected]> <[email protected]> > > <mailto:[email protected]> > > <mailto:[email protected]> > > <mailto:[email protected]> > > > Subject: Increasing degree of parallelism > > when reading > > Parquet files > > > > > > > > > > > > EXTERNAL EMAIL: Use caution when > > opening attachments > > or clicking on > > links > > > > > > > > > > > > > > > > > > Dear AsterixDB devs, > > > > > > > > > > > > I am currently trying out the new support > > for Parquet files > > on S3 (still in the > > > context of my High-energy Physics use case > > [1]). This works > > great so far and > > has > > > generally decent performance. However, I > > realized that it > > does not use more > > > than 16 cores, even though 96 logical > > cores > > are available > > and even though I > > run > > > long-running queries (several minutes) on > > large data sets > > with a large > > number of > > > files (I tried 128 files of 17GB each). > > Is this > > an > > arbitrary/artificial limitation > > that > > > can be changed somehow (potentially with > > a small > > patch+recompiling) or is > > > there more serious development required > > to lift it? FYI, I am > > currently using > > > 03fd6d0f, which should include all > > S3/Parquet commits on > > master. > > > > > > > > > > > > Cheers, > > > > > > Ingo > > > > > > > > > > > > > > > > > > [1] https://arxiv.org/abs/2104.12615 > > > > > > > > > > > > > > > >
