=item 2
-Process spawning
+Optional Inline::C use
=item 3
Read-only daemons
+=item 7
+
+Other OS tuning knobs
+
+=item 8
+
+Scalability to many inboxes
+
=back
=head2 New inboxes: public-inbox-init -V2
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
+=head2 Optional Inline::C use
Our optional use of L<Inline::C> speeds up subprocess spawning from
large daemon processes.
C<~/.cache/public-inbox/inline-c> for any user(s) running
public-inbox processes.
+If libgit2 development files are installed and L<Inline::C>
+is enabled (described above), per-inbox C<git cat-file --batch>
+processes are replaced with a single L<perl(1)> process running
+C<PublicInbox::Gcf2::loop> in read-only daemons. libgit2 use
+will be available in public-inbox 1.7.0+
+
More (optional) L<Inline::C> use will be introduced in the future
to lower memory use and improve scalability.
+Note: L<Inline::C> is required for L<lei(1)>, but not public-inbox-*
+
=head2 Performance on rotational hard disk drives
Random I/O performance is poor on rotational HDDs. Xapian indexing
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.
+reduce its kernel page cache footprint. Keep in mind excessive
+sharding imposes a performance penalty for read-only queries.
Users with large amounts of RAM are advised to set a large value
for C<publicinbox.indexBatchSize> as documented in
-L<public-inbox-config(5)>.
+L<public-inbox-index(1)>.
C<dm-crypt> users on Linux 4.0+ are advised to try the
C<--perf-same_cpu_crypt> C<--perf-submit_from_crypt_cpus>
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.
+Disabling copy-on-write also disables checksumming, thus C<raid1>
+(or higher) configurations may be corrupt after unsafe shutdowns.
Fortunately, these SQLite and Xapian indices are designed to
recoverable from git if missing.
+Disabling CoW does not prevent all fragmentation. Large values
+of C<publicInbox.indexBatchSize> also limit fragmentation during
+the initial index.
+
+Avoid snapshotting subvolumes containing Xapian and/or SQLite indices.
+Snapshots use CoW despite our efforts to disable it, resulting
+in fragmentation.
+
+L<filefrag(8)> can be used to monitor fragmentation, and
+C<btrfs filesystem defragment -fr $INBOX_DIR> may be necessary.
+
Large filesystems benefit significantly from the C<space_cache=v2>
mount option documented in L<btrfs(5)>.
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.
+Users of the Flash-Friendly File System
+L<F2FS|https://en.wikipedia.org/wiki/F2FS> may benefit from
+optimizations found in SQLite 3.21.0+. Benchmarks are greatly
+appreciated.
+
=head2 Read-only daemons
L<public-inbox-httpd(1)>, L<public-inbox-imapd(1)>, and
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.
+accommodate 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.
+=head2 Other OS tuning knobs
+
+Linux users: the C<sys.vm.max_map_count> sysctl may need to be increased if
+handling thousands of inboxes (with L<public-inbox-extindex(1)>) to avoid
+out-of-memory errors from git.
+
+Other OSes may have similar tuning knobs (patches appreciated).
+
+=head2 Scalability to many inboxes
+
+L<public-inbox-extindex(1)> allows any number of public-inboxes
+to share the same Xapian indices.
+
+git 2.33+ startup time is orders-of-magnitude faster and uses
+less memory when dealing with thousands of alternates required
+for thousands of inboxes with L<public-inbox-extindex(1)>.
+
+Frequent packing (via L<git-gc(1)>) both improves performance
+and reduces the need to increase C<sys.vm.max_map_count>.
+
=head1 CONTACT
Feedback encouraged via plain-text mail to L<mailto:meta@public-inbox.org>
welcome.
Our archives are hosted at L<https://public-inbox.org/meta/>,
-L<http://hjrcffqmbrq6wope.onion/meta/>, and other places
+L<http://4uok3hntl7oi7b4uf4rtfwefqeexfzil2w6kgk2jn5z2f764irre7byd.onion/meta/>, and other places
=head1 COPYRIGHT
-Copyright 2020 all contributors L<mailto:meta@public-inbox.org>
+Copyright all contributors L<mailto:meta@public-inbox.org>
License: AGPL-3.0+ L<https://www.gnu.org/licenses/agpl-3.0.txt>