doc: add some recommendations around slow HDDs

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

diff --git a/Documentation/public-inbox-index.pod b/Documentation/public-inbox-index.pod
index 398ac516bf9c729ff595cc0d810749faa85091df..ff2e5486748889667667de1ef0f86d0d6f390115 100644 (file)
--- a/Documentation/public-inbox-index.pod
+++ b/Documentation/public-inbox-index.pod
@@ -32,6 +32,16 @@ normal search functionality.
 
 =over
 
+=item --jobs=JOBS, -j
+
+Control the number of Xapian indexing jobs in a
+(L<public-inbox-v2-format(5)>) inbox.
+
+C<--jobs=0> is accepted as of public-inbox 1.6.0 (PENDING)
+to disable parallel indexing.
+
+Default: the number of existing Xapian shards
+
 =item --compact / -c
 
 Compacts the Xapian DBs after indexing.  This is recommended
@@ -46,6 +56,8 @@ This switch may be specified twice, in which case compaction
 happens both before and after indexing to minimize the temporal
 footprint of the (re)indexing operation.
 
+Available since public-inbox 1.4.0.
+
 =item --reindex
 
 Forces a re-index of all messages in the inbox.
@@ -56,6 +68,10 @@ Xapian database.  Using this with C<--compact> or running
 L<public-inbox-compact(1)> afterwards is recommended to
 release free space.
 
+public-inbox protects writes to various indices with L<flock(2)>,
+so it is safe to reindex while L<public-inbox-watch(1)>,
+L<public-inbox-mda(1)> or L<public-inbox-learn(1)> run.
+
 This does not touch the NNTP article number database or
 affect threading.
 
@@ -66,12 +82,24 @@ is detected.  This is intended to be used in mirrors after running
 L<public-inbox-edit(1)> or L<public-inbox-purge(1)> to ensure data
 is expunged from mirrors.
 
+Available since public-inbox 1.2.0.
+
 =item --max-size SIZE
 
 Sets or overrides L</publicinbox.indexMaxSize> on a
 per-invocation basis.  See L</publicinbox.indexMaxSize>
 below.
 
+Available since public-inbox 1.5.0.
+
+=item --batch-size SIZE
+
+Sets or overrides L</publicinbox.indexBatchSize> on a
+per-invocation basis.  See L</publicinbox.indexBatchSize>
+below.
+
+Available in public-inbox 1.6.0 (PENDING).
+
 =back
 
 =head1 FILES
@@ -94,9 +122,31 @@ supported, thus the value of C<1m> to prevents indexing of
 messages larger than one megabyte.
 
 This is useful for avoiding memory exhaustion in mirrors.
+This option is only available in public-inbox 1.5 or later.
 
 Default: none
 
+=item publicinbox.indexBatchSize
+
+Flushes changes to the filesystem and releases locks after
+indexing the given number of bytes.  The default value of C<1m>
+(one megabyte) is low to minimize memory use and reduce
+contention with parallel invocations of L<public-inbox-mda(1)>,
+L<public-inbox-learn(1)>, and L<public-inbox-watch(1)>.
+
+Increase this value on powerful systems to improve throughput at
+the expense of memory use.  The reduction of lock granularity
+may not be noticeable on fast systems.
+
+This option is available in public-inbox 1.6 or later.
+public-inbox 1.5 and earlier used the current default, C<1m>.
+
+For L<public-inbox-v2-format(5)> inboxes, this value is
+multiplied by the number of Xapian shards.  Thus a typical v2
+inbox with 3 shards will flush every 3 megabytes by default.
+
+Default: 1m (one megabyte)
+
 =back
 
 =head1 ENVIRONMENT
@@ -113,10 +163,13 @@ The number of documents to update before committing changes to
 disk.  This environment is handled directly by Xapian, refer to
 Xapian API documentation for more details.
 
-Default: our indexing code flushes every megabyte of mail seen
-to keep memory usage low.  Setting this environment variable to
-any positive value will switch to a document count-based
-threshold in Xapian.
+For public-inbox 1.6 and later, use C<publicinbox.indexBatchSize>
+instead.  Setting C<XAPIAN_FLUSH_THRESHOLD> for a large C<--reindex>
+may cause L<public-inbox-mda(1)>, L<public-inbox-learn(1)> and
+L<public-inbox-watch(1)> tasks to wait long periods of time
+during C<--reindex>.
+
+Default: none, uses C<publicinbox.indexBatchSize>
 
 =back