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* [PATCH] doc: add public-inbox-tuning(7) manpage
@ 2020-08-15  5:21 Eric Wong
  0 siblings, 0 replies; only message in thread
From: Eric Wong @ 2020-08-15  5:21 UTC (permalink / raw)
  To: meta

Determining storage device speed and latencies doesn't
seem portable or even possible with the wide variety
of storage layers in use.

This means we need to write a tuning document and hope
users read and improve on it :P
 Documentation/public-inbox-tuning.pod    | 139 +++++++++++++++++++++++
 Documentation/public-inbox-v2-format.pod |   6 +-
 MANIFEST                                 |   1 +
 Makefile.PL                              |   2 +-
 4 files changed, 144 insertions(+), 4 deletions(-)
 create mode 100644 Documentation/public-inbox-tuning.pod

diff --git a/Documentation/public-inbox-tuning.pod b/Documentation/public-inbox-tuning.pod
new file mode 100644
index 00000000..abc53d1e
--- /dev/null
+++ b/Documentation/public-inbox-tuning.pod
@@ -0,0 +1,139 @@
+=head1 NAME
+public-inbox-tuning - tuning public-inbox
+public-inbox intends to support a wide variety of hardware.  While
+we strive to provide the best out-of-the-box performance possible,
+tuning knobs are an unfortunate necessity in some cases.
+=over 4
+=item 1
+New inboxes: public-inbox-init -V2
+=item 2
+Process spawning
+=item 3
+Performance on rotational hard disk drives
+=item 4
+Btrfs (and possibly other copy-on-write filesystems)
+=item 5
+Performance on solid state drives
+=item 6
+Read-only daemons
+=head2 New inboxes: public-inbox-init -V2
+If you're starting a new inbox (and not mirroring an existing one),
+the L<-V2|public-inbox-v2-format(5)> requires L<DBD::SQLite>, but is
+orders of magnitude more scalable than the original C<-V1> format.
+=head2 Process spawning
+Our optional use of L<Inline::C> speeds up subprocess spawning from
+large daemon processes.
+To enable L<Inline::C>, either set the C<PERL_INLINE_DIRECTORY>
+environment variable to point to a writable directory, or create
+C<~/.cache/public-inbox/inline-c> for any user(s) running
+public-inbox processes.
+More (optional) L<Inline::C> use will be introduced in the future
+to lower memory use and improve scalability.
+=head2 Performance on rotational hard disk drives
+Random I/O performance is poor on rotational HDDs.  Xapian indexing
+performance degrades significantly as DBs grow larger than available
+RAM.  Attempts to parallelize random I/O on HDDs leads to pathological
+slowdowns as inboxes grow.
+While C<-V2> introduced Xapian shards as a parallelization
+mechanism for SSDs; enabling C<publicInbox.indexSequentialShard>
+repurposes sharding as mechanism to reduce the kernel page cache
+footprint when indexing on HDDs.
+Initializing a mirror with a high C<--jobs> count to create more
+shards (in C<-V2> inboxes) will keep each shard smaller and
+reduce its kernel page cache footprint.
+Users with large amounts of RAM are advised to set a large value
+for C<publicinbox.indexBatchSize> as documented in
+C<dm-crypt> users on Linux 4.0+ are advised to try the
+C<--perf-same_cpu_crypt> C<--perf-submit_from_crypt_cpus>
+switches of L<cryptsetup(8)> to reduce I/O contention from
+kernel workqueue threads.
+=head2 Btrfs (and possibly other copy-on-write filesystems)
+L<btrfs(5)> performance degrades from fragmentation when using
+large databases and random writes.  The Xapian + SQLite indices
+used by public-inbox are no exception to that.
+public-inbox 1.6.0+ disables copy-on-write (CoW) on Xapian and SQLite
+indices on btrfs to achieve acceptable performance (even on SSD).
+Disabling copy-on-write also disables checksumming, thus raid1
+(or higher) configurations may corrupt on unsafe shutdowns.
+Fortunately, these SQLite and Xapian indices are designed to
+recoverable from git if missing.
+Large filesystems benefit significantly from the C<space_cache=v2>
+mount option documented in L<btrfs(5)>.
+Older, non-CoW filesystems are generally work well out-of-the-box
+for our Xapian and SQLite indices.
+=head2 Performance on solid state drives
+While SSD read performance is generally good, SSD write performance
+degrades as the drive ages and/or gets full.  Issuing C<TRIM> commands
+via L<fstrim(8)> or similar is required to sustain write performance.
+=head2 Read-only daemons
+L<public-inbox-httpd(1)>, L<public-inbox-imapd(1)>, and
+L<public-inbox-nntpd(1)> are all designed for C10K (or higher)
+levels of concurrency from a single process.  SMP systems may
+use C<--worker-processes=NUM> as documented in L<public-inbox-daemon(8)>
+for parallelism.
+The open file descriptor limit (C<RLIMIT_NOFILE>, C<ulimit -n> in L<sh(1)>,
+C<LimitNOFILE=> in L<systemd.exec(5)>) may need to be raised to
+accomodate many concurrent clients.
+Transport Layer Security (IMAPS, NNTPS, or via STARTTLS) significantly
+increases memory use of client sockets, sure to account for that in
+capacity planning.
+=head1 CONTACT
+Feedback encouraged via plain-text mail to L<>
+Information for *BSDs and non-traditional filesystems especially
+Our archives are hosted at L<>,
+L<http://hjrcffqmbrq6wope.onion/meta/>, and other places
+Copyright 2020 all contributors L<>
+License: AGPL-3.0+ L<>
diff --git a/Documentation/public-inbox-v2-format.pod b/Documentation/public-inbox-v2-format.pod
index 6876989c..86a9b8f2 100644
--- a/Documentation/public-inbox-v2-format.pod
+++ b/Documentation/public-inbox-v2-format.pod
@@ -117,9 +117,9 @@ Rotational storage devices perform significantly worse than
 solid state storage for indexing of large mail archives; but are
 fine for backup and usable for small instances.
-As of public-inbox 1.6.0, the C<--sequential-shard> option of
-L<public-inbox-index(1)> may be used with a high shard count
-to ensure individual shards fit into page cache when the entire
+As of public-inbox 1.6.0, the C<publicInbox.indexSequentialShard>
+option of L<public-inbox-index(1)> may be used with a high shard
+count to ensure individual shards fit into page cache when the entire
 Xapian DB cannot.
 Our use of the L</OVERVIEW DB> requires Xapian document IDs to
diff --git a/MANIFEST b/MANIFEST
index 3d690177..6cb5f6bf 100644
@@ -35,6 +35,7 @@ Documentation/public-inbox-mda.pod
diff --git a/Makefile.PL b/Makefile.PL
index 831649f9..88da5b45 100644
--- a/Makefile.PL
+++ b/Makefile.PL
@@ -34,7 +34,7 @@ $v->{my_syntax} = [map { "$_.syntax" } @syn];
 $v->{-m1} = [ map { (split('/'))[-1] } @EXE_FILES ];
 $v->{-m5} = [ qw(public-inbox-config public-inbox-v1-format
 		public-inbox-v2-format) ];
-$v->{-m7} = [ qw(public-inbox-overview) ];
+$v->{-m7} = [ qw(public-inbox-overview public-inbox-tuning) ];
 $v->{-m8} = [ qw(public-inbox-daemon) ];
 my @sections = (1, 5, 7, 8);
 $v->{check_80} = [];

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2020-08-15  5:21 [PATCH] doc: add public-inbox-tuning(7) manpage Eric Wong

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