doc: speling fickses

[public-inbox.git] / Documentation / public-inbox-tuning.pod

diff --git a/Documentation/public-inbox-tuning.pod b/Documentation/public-inbox-tuning.pod
index abc53d1ee0722c7561190bc805dcf5b4e6b81993..b4e7698bcca975a972921216128d74225cb222f9 100644 (file)
--- a/Documentation/public-inbox-tuning.pod
+++ b/Documentation/public-inbox-tuning.pod
@@ -69,7 +69,8 @@ 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
 
 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
 
 Users with large amounts of RAM are advised to set a large value
 for C<publicinbox.indexBatchSize> as documented in


@@ -88,12 +89,21 @@ 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).
 
 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.
 
 
 Fortunately, these SQLite and Xapian indices are designed to
 recoverable from git if missing.
 

+Disabling CoW does not prevent all fragmentation.
+
+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)>.
 
 Large filesystems benefit significantly from the C<space_cache=v2>
 mount option documented in L<btrfs(5)>.
 


@@ -106,6 +116,11 @@ 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.
 
 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
 =head2 Read-only daemons
 
 L<public-inbox-httpd(1)>, L<public-inbox-imapd(1)>, and


@@ -116,7 +131,7 @@ 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
 
 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
 
 Transport Layer Security (IMAPS, NNTPS, or via STARTTLS) significantly
 increases memory use of client sockets, sure to account for that in