RE: [PoC] Non-volatile WAL buffer

Dear hackers,

I update my non-volatile WAL buffer's patchset to v3. Now we can use it in streaming replication mode.

Updates from v2:

- walreceiver supports non-volatile WAL buffer
Now walreceiver stores received records directly to non-volatile WAL buffer if applicable.

- pg_basebackup supports non-volatile WAL buffer
Now pg_basebackup copies received WAL segments onto non-volatile WAL buffer if you run it with "nvwal" mode (-Fn).
You should specify a new NVWAL path with --nvwal-path option. The path will be written to postgresql.auto.conf or recovery.conf. The size of the new NVWAL is same as the master's one.

Best regards,
Takashi

--
Takashi Menjo <takashi(dot)menjou(dot)vg(at)hco(dot)ntt(dot)co(dot)jp>
NTT Software Innovation Center

> -----Original Message-----
> From: Takashi Menjo <takashi(dot)menjou(dot)vg(at)hco(dot)ntt(dot)co(dot)jp>
> Sent: Wednesday, March 18, 2020 5:59 PM
> To: 'PostgreSQL-development' <pgsql-hackers(at)postgresql(dot)org>
> Cc: 'Robert Haas' <robertmhaas(at)gmail(dot)com>; 'Heikki Linnakangas' <hlinnaka(at)iki(dot)fi>; 'Amit Langote'
> <amitlangote09(at)gmail(dot)com>
> Subject: RE: [PoC] Non-volatile WAL buffer
>
> Dear hackers,
>
> I rebased my non-volatile WAL buffer's patchset onto master. A new v2 patchset is attached to this mail.
>
> I also measured performance before and after patchset, varying -c/--client and -j/--jobs options of pgbench, for
> each scaling factor s = 50 or 1000. The results are presented in the following tables and the attached charts.
> Conditions, steps, and other details will be shown later.
>
>
> Results (s=50)
> ==============
> Throughput [10^3 TPS] Average latency [ms]
> ( c, j) before after before after
> ------- --------------------- ---------------------
> ( 8, 8) 35.7 37.1 (+3.9%) 0.224 0.216 (-3.6%)
> (18,18) 70.9 74.7 (+5.3%) 0.254 0.241 (-5.1%)
> (36,18) 76.0 80.8 (+6.3%) 0.473 0.446 (-5.7%)
> (54,18) 75.5 81.8 (+8.3%) 0.715 0.660 (-7.7%)
>
>
> Results (s=1000)
> ================
> Throughput [10^3 TPS] Average latency [ms]
> ( c, j) before after before after
> ------- --------------------- ---------------------
> ( 8, 8) 37.4 40.1 (+7.3%) 0.214 0.199 (-7.0%)
> (18,18) 79.3 86.7 (+9.3%) 0.227 0.208 (-8.4%)
> (36,18) 87.2 95.5 (+9.5%) 0.413 0.377 (-8.7%)
> (54,18) 86.8 94.8 (+9.3%) 0.622 0.569 (-8.5%)
>
>
> Both throughput and average latency are improved for each scaling factor. Throughput seemed to almost reach
> the upper limit when (c,j)=(36,18).
>
> The percentage in s=1000 case looks larger than in s=50 case. I think larger scaling factor leads to less
> contentions on the same tables and/or indexes, that is, less lock and unlock operations. In such a situation,
> write-ahead logging appears to be more significant for performance.
>
>
> Conditions
> ==========
> - Use one physical server having 2 NUMA nodes (node 0 and 1)
> - Pin postgres (server processes) to node 0 and pgbench to node 1
> - 18 cores and 192GiB DRAM per node
> - Use an NVMe SSD for PGDATA and an interleaved 6-in-1 NVDIMM-N set for pg_wal
> - Both are installed on the server-side node, that is, node 0
> - Both are formatted with ext4
> - NVDIMM-N is mounted with "-o dax" option to enable Direct Access (DAX)
> - Use the attached postgresql.conf
> - Two new items nvwal_path and nvwal_size are used only after patch
>
>
> Steps
> =====
> For each (c,j) pair, I did the following steps three times then I found the median of the three as a final result shown
> in the tables above.
>
> (1) Run initdb with proper -D and -X options; and also give --nvwal-path and --nvwal-size options after patch
> (2) Start postgres and create a database for pgbench tables
> (3) Run "pgbench -i -s ___" to create tables (s = 50 or 1000)
> (4) Stop postgres, remount filesystems, and start postgres again
> (5) Execute pg_prewarm extension for all the four pgbench tables
> (6) Run pgbench during 30 minutes
>
>
> pgbench command line
> ====================
> $ pgbench -h /tmp -p 5432 -U username -r -M prepared -T 1800 -c ___ -j ___ dbname
>
> I gave no -b option to use the built-in "TPC-B (sort-of)" query.
>
>
> Software
> ========
> - Distro: Ubuntu 18.04
> - Kernel: Linux 5.4 (vanilla kernel)
> - C Compiler: gcc 7.4.0
> - PMDK: 1.7
> - PostgreSQL: d677550 (master on Mar 3, 2020)
>
>
> Hardware
> ========
> - System: HPE ProLiant DL380 Gen10
> - CPU: Intel Xeon Gold 6154 (Skylake) x 2sockets
> - DRAM: DDR4 2666MHz {32GiB/ch x 6ch}/socket x 2sockets
> - NVDIMM-N: DDR4 2666MHz {16GiB/ch x 6ch}/socket x 2sockets
> - NVMe SSD: Intel Optane DC P4800X Series SSDPED1K750GA
>
>
> Best regards,
> Takashi
>
> --
> Takashi Menjo <takashi(dot)menjou(dot)vg(at)hco(dot)ntt(dot)co(dot)jp> NTT Software Innovation Center
>
> > -----Original Message-----
> > From: Takashi Menjo <takashi(dot)menjou(dot)vg(at)hco(dot)ntt(dot)co(dot)jp>
> > Sent: Thursday, February 20, 2020 6:30 PM
> > To: 'Amit Langote' <amitlangote09(at)gmail(dot)com>
> > Cc: 'Robert Haas' <robertmhaas(at)gmail(dot)com>; 'Heikki Linnakangas' <hlinnaka(at)iki(dot)fi>;
> 'PostgreSQL-development'
> > <pgsql-hackers(at)postgresql(dot)org>
> > Subject: RE: [PoC] Non-volatile WAL buffer
> >
> > Dear Amit,
> >
> > Thank you for your advice. Exactly, it's so to speak "do as the hackers do when in pgsql"...
> >
> > I'm rebasing my branch onto master. I'll submit an updated patchset and performance report later.
> >
> > Best regards,
> > Takashi
> >
> > --
> > Takashi Menjo <takashi(dot)menjou(dot)vg(at)hco(dot)ntt(dot)co(dot)jp> NTT Software
> > Innovation Center
> >
> > > -----Original Message-----
> > > From: Amit Langote <amitlangote09(at)gmail(dot)com>
> > > Sent: Monday, February 17, 2020 5:21 PM
> > > To: Takashi Menjo <takashi(dot)menjou(dot)vg(at)hco(dot)ntt(dot)co(dot)jp>
> > > Cc: Robert Haas <robertmhaas(at)gmail(dot)com>; Heikki Linnakangas
> > > <hlinnaka(at)iki(dot)fi>; PostgreSQL-development
> > > <pgsql-hackers(at)postgresql(dot)org>
> > > Subject: Re: [PoC] Non-volatile WAL buffer
> > >
> > > Hello,
> > >
> > > On Mon, Feb 17, 2020 at 4:16 PM Takashi Menjo <takashi(dot)menjou(dot)vg(at)hco(dot)ntt(dot)co(dot)jp> wrote:
> > > > Hello Amit,
> > > >
> > > > > I apologize for not having any opinion on the patches
> > > > > themselves, but let me point out that it's better to base these
> > > > > patches on HEAD (master branch) than REL_12_0, because all new
> > > > > code is committed to the master branch, whereas stable branches
> > > > > such as
> > > > > REL_12_0 only receive bug fixes. Do you have any
> > > specific reason to be working on REL_12_0?
> > > >
> > > > Yes, because I think it's human-friendly to reproduce and discuss
> > > > performance measurement. Of course I know
> > > all new accepted patches are merged into master's HEAD, not stable
> > > branches and not even release tags, so I'm aware of rebasing my
> > > patchset onto master sooner or later. However, if someone,
> > > including me, says that s/he applies my patchset to "master" and
> > > measures its performance, we have to pay attention to which commit the "master"
> > > really points to. Although we have sha1 hashes to specify which
> > > commit, we should check whether the specific commit on master has
> > > patches affecting performance or not
> > because master's HEAD gets new patches day by day. On the other hand,
> > a release tag clearly points the commit all we probably know. Also we
> > can check more easily the features and improvements by using release notes and user manuals.
> > >
> > > Thanks for clarifying. I see where you're coming from.
> > >
> > > While I do sometimes see people reporting numbers with the latest
> > > stable release' branch, that's normally just one of the baselines.
> > > The more important baseline for ongoing development is the master
> > > branch's HEAD, which is also what people volunteering to test your
> > > patches would use. Anyone who reports would have to give at least
> > > two numbers -- performance with a branch's HEAD without patch
> > > applied and that with patch applied -- which can be enough in most
> > > cases to see the difference the patch makes. Sure, the numbers
> > > might change on each report, but that's fine I'd think. If you
> > > continue to develop against the stable branch, you might miss to
> > notice impact from any relevant developments in the master branch,
> > even developments which possibly require rethinking the architecture of your own changes, although maybe that
> rarely occurs.
> > >
> > > Thanks,
> > > Amit