NAME

       public-inbox-tuning - tuning public-inbox

DESCRIPTION

       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.

       1.  New inboxes: public-inbox-init -V2

       2.  Optional Inline::C use

       3.  Performance on rotational hard disk drives

       4.  Btrfs (and possibly other copy-on-write filesystems)

       5.  Performance on solid state drives

       6.  Read-only daemons

       7.  Other OS tuning knobs

       8.  Scalability to many inboxes

   New inboxes: public-inbox-init -V2
       If you're starting a new inbox (and not mirroring an existing one), the -V2 requires
       DBD::SQLite, but is orders of magnitude more scalable than the original "-V1" format.

   Optional Inline::C use
       Our optional use of Inline::C speeds up subprocess spawning from large daemon processes.

       To enable Inline::C, either set the "PERL_INLINE_DIRECTORY" environment variable to point
       to a writable directory, or create "~/.cache/public-inbox/inline-c" for any user(s)
       running public-inbox processes.

       If libgit2 development files are installed and Inline::C is enabled (described above),
       per-inbox "git cat-file --batch" processes are replaced with a single perl(1) process
       running "PublicInbox::Gcf2::loop" in read-only daemons.  libgit2 use will be available in
       public-inbox 1.7.0+

       More (optional) Inline::C use will be introduced in the future to lower memory use and
       improve scalability.

       Note: Inline::C is required for lei(1), but not public-inbox-*

   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 "-V2" introduced Xapian shards as a parallelization mechanism for SSDs; enabling
       "publicInbox.indexSequentialShard" repurposes sharding as mechanism to reduce the kernel
       page cache footprint when indexing on HDDs.

       Initializing a mirror with a high "--jobs" count to create more shards (in "-V2" inboxes)
       will keep each shard smaller and 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
       "publicinbox.indexBatchSize" as documented in public-inbox-index(1).

       "dm-crypt" users on Linux 4.0+ are advised to try the "--perf-same_cpu_crypt"
       "--perf-submit_from_crypt_cpus" switches of cryptsetup(8) to reduce I/O contention from
       kernel workqueue threads.

   Btrfs (and possibly other copy-on-write filesystems)
       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 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
       "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.

       filefrag(8) can be used to monitor fragmentation, and "btrfs filesystem defragment -fr
       $INBOX_DIR" may be necessary.

       Large filesystems benefit significantly from the "space_cache=v2" mount option documented
       in btrfs(5).

       Older, non-CoW filesystems are generally work well out-of-the-box for our Xapian and
       SQLite indices.

   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 "TRIM" commands via fstrim(8) or similar is required to
       sustain write performance.

       Users of the Flash-Friendly File System F2FS <https://en.wikipedia.org/wiki/F2FS> may
       benefit from optimizations found in SQLite 3.21.0+.  Benchmarks are greatly appreciated.

   Read-only daemons
       public-inbox-httpd(1), public-inbox-imapd(1), and public-inbox-nntpd(1) are all designed
       for C10K (or higher) levels of concurrency from a single process.  SMP systems may use
       "--worker-processes=NUM" as documented in public-inbox-daemon(8) for parallelism.

       The open file descriptor limit ("RLIMIT_NOFILE", "ulimit -n" in sh(1), "LimitNOFILE=" in
       systemd.exec(5)) may need to be raised to 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.

   Other OS tuning knobs
       Linux users: the "sys.vm.max_map_count" sysctl may need to be increased if handling
       thousands of inboxes (with public-inbox-extindex(1)) to avoid out-of-memory errors from
       git.

       Other OSes may have similar tuning knobs (patches appreciated).

   Scalability to many inboxes
       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
       public-inbox-extindex(1).

       Frequent packing (via git-gc(1)) both improves performance and reduces the need to
       increase "sys.vm.max_map_count".

CONTACT

       Feedback encouraged via plain-text mail to <mailto:meta@public-inbox.org>

       Information for *BSDs and non-traditional filesystems especially welcome.

       Our archives are hosted at <https://public-inbox.org/meta/>,
       <http://4uok3hntl7oi7b4uf4rtfwefqeexfzil2w6kgk2jn5z2f764irre7byd.onion/meta/>, and other
       places

COPYRIGHT

       Copyright all contributors <mailto:meta@public-inbox.org>

       License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>