doc: expand on indexBatchSize regarding fragmentation

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

diff --git a/Documentation/public-inbox-index.pod b/Documentation/public-inbox-index.pod
index aeb1b3a39fbfaf9c4da3144c3f18b98014774895..936516f808eaa52b15b4248a2ea91317cfbfae8d 100644 (file)
--- a/Documentation/public-inbox-index.pod
+++ b/Documentation/public-inbox-index.pod
@@ -6,6 +6,8 @@ public-inbox-index - create and update search indices
 
 public-inbox-index [OPTIONS] INBOX_DIR...
 
 
 public-inbox-index [OPTIONS] INBOX_DIR...
 

+public-inbox-index [OPTIONS] --all
+

 =head1 DESCRIPTION
 
 public-inbox-index creates and updates the search, overview and
 =head1 DESCRIPTION
 
 public-inbox-index creates and updates the search, overview and


@@ -34,11 +36,19 @@ normal search functionality.
 
 =item --jobs=JOBS, -j
 
 
 =item --jobs=JOBS, -j
 

-Control the number of Xapian indexing jobs in a
+Influences the number of Xapian indexing shards in a

 (L<public-inbox-v2-format(5)>) inbox.
 
 (L<public-inbox-v2-format(5)>) inbox.
 

+See L<public-inbox-init(1)/--jobs> for a full description
+of sharding.
+

 C<--jobs=0> is accepted as of public-inbox 1.6.0 (PENDING)
 C<--jobs=0> is accepted as of public-inbox 1.6.0 (PENDING)

-to disable parallel indexing.
+to disable parallel indexing regardless of the number of
+pre-existing shards.
+
+If the inbox has not been indexed or initialized, C<JOBS - 1>
+shards will be created (one job is always needed for indexing
+the overview and article number mapping).

 
 Default: the number of existing Xapian shards
 
 
 Default: the number of existing Xapian shards
 


@@ -77,6 +87,12 @@ This does not touch the NNTP article number database.
 It does not affect threading unless C<--rethread> is
 used.
 
 It does not affect threading unless C<--rethread> is
 used.
 

+=item --all
+
+Index all inboxes configured in ~/.public-inbox/config.
+This is an alternative to specifying individual inboxes directories
+on the command-line.
+

 =item --rethread
 
 Regenerate internal THREADID and message thread associations
 =item --rethread
 
 Regenerate internal THREADID and message thread associations


@@ -111,12 +127,38 @@ Sets or overrides L</publicinbox.indexBatchSize> on a
 per-invocation basis.  See L</publicinbox.indexBatchSize>
 below.
 
 per-invocation basis.  See L</publicinbox.indexBatchSize>
 below.
 

+When using rotational storage but abundant RAM, using a large
+value (e.g. C<500m>) with C<--sequential-shard> can
+significantly speed up and reduce fragmentation during the
+initial index and full C<--reindex> invocations (but not
+incremental updates).
+

 Available in public-inbox 1.6.0 (PENDING).
 
 Available in public-inbox 1.6.0 (PENDING).
 

-=item --no-sync
+=item --no-fsync

 
 Disables L<fsync(2)> and L<fdatasync(2)> operations on SQLite
 
 Disables L<fsync(2)> and L<fdatasync(2)> operations on SQLite

-and Xapian.  This is only effective with Xapian 1.4+.
+and Xapian.  This is only effective with Xapian 1.4+.  This is
+primarily intended for systems with low RAM and the small
+(default) C<--batch-size=1m>.  Users of large C<--batch-size>
+may even find disabling L<fdatasync(2)> causes too much dirty
+data to accumulate, resulting on latency spikes from writeback.
+
+Available in public-inbox 1.6.0 (PENDING).
+
+=item --sequential-shard
+
+Sets or overrides L</publicinbox.indexSequentialShard> on a
+per-invocation basis.  See L</publicinbox.indexSequentialShard>
+below.
+
+Available in public-inbox 1.6.0 (PENDING).
+
+=item --skip-docdata
+
+Stop storing document data in Xapian on an existing inbox.
+
+See L<public-inbox-init(1)/--skip-docdata> for description and caveats.

 
 Available in public-inbox 1.6.0 (PENDING).
 
 
 Available in public-inbox 1.6.0 (PENDING).
 


@@ -124,11 +166,11 @@ Available in public-inbox 1.6.0 (PENDING).
 
 =head1 FILES
 
 
 =head1 FILES
 

-For v1 (ssoma) repositories described in L<public-inbox-v1-format>.
+For v1 (ssoma) repositories described in L<public-inbox-v1-format(5)>.

 All public-inbox-specific files are contained within the
 C<$GIT_DIR/public-inbox/> directory.
 
 All public-inbox-specific files are contained within the
 C<$GIT_DIR/public-inbox/> directory.
 

-v2 inboxes are described in L<public-inbox-v2-format>.
+v2 inboxes are described in L<public-inbox-v2-format(5)>.

 
 =head1 CONFIGURATION
 
 
 =head1 CONFIGURATION
 


@@ -141,7 +183,11 @@ value.  A single suffix modifier of C<k>, C<m> or C<g> is
 supported, thus the value of C<1m> to prevents indexing of
 messages larger than one megabyte.
 
 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 is useful for avoiding memory exhaustion in mirrors
+via git.  It does not prevent L<public-inbox-mda(1)> or
+L<public-inbox-watch(1)> from importing (and indexing)
+a message.
+

 This option is only available in public-inbox 1.5 or later.
 
 Default: none
 This option is only available in public-inbox 1.5 or later.
 
 Default: none


@@ -156,17 +202,52 @@ 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
 
 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>.
+may not be noticeable on fast systems.  With SSDs, values above
+C<4m> have little benefit.

 
 For L<public-inbox-v2-format(5)> inboxes, this value is
 multiplied by the number of Xapian shards.  Thus a typical v2
 
 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.
+inbox with 3 shards will flush every 3 megabytes by default
+unless parallelism is disabled via C<--sequential-shard>
+or C<--jobs=0>.
+
+This influences memory usage of Xapian, but it is not exact.
+The actual memory used by Xapian and Perl has been observed
+in excess of 10x this value.
+
+This option is available in public-inbox 1.6 or later.
+public-inbox 1.5 and earlier used the current default, C<1m>.

 
 Default: 1m (one megabyte)
 
 
 Default: 1m (one megabyte)
 

+=item publicinbox.indexSequentialShard
+
+For L<public-inbox-v2-format(5)> inboxes, setting this to C<true>
+allows indexing Xapian shards in multiple passes.  This speeds up
+indexing on rotational storage with high seek latency by allowing
+individual shards to fit into the kernel page cache.
+
+Using a higher-than-normal number of C<--jobs> with
+L<public-inbox-init(1)> may be required to ensure individual
+shards are small enough to fit into cache.
+
+Warning: interrupting C<public-inbox-index(1)> while this option
+is in use may leave the search indices out-of-date with respect
+to SQLite databases.  WWW and IMAP users may notice incomplete
+search results, but it is otherwise non-fatal.  Using C<--reindex>
+will bring everything back up-to-date.
+
+Available in public-inbox 1.6.0 (PENDING).
+
+This is ignored on L<public-inbox-v1-format(5)> inboxes.
+
+Default: false, shards are indexed in parallel
+
+=item publicinbox.<name>.indexSequentialShard
+
+Identical to L</publicinbox.indexSequentialShard>,
+but only affect the inbox matching E<lt>nameE<gt>.
+

 =back
 
 =head1 ENVIRONMENT
 =back
 
 =head1 ENVIRONMENT


@@ -184,10 +265,13 @@ disk.  This environment is handled directly by Xapian, refer to
 Xapian API documentation for more details.
 
 For public-inbox 1.6 and later, use C<publicinbox.indexBatchSize>
 Xapian API documentation for more details.
 
 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>.
+instead.
+
+Setting C<XAPIAN_FLUSH_THRESHOLD> or
+C<publicinbox.indexBatchSize> 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 and unpredictable
+periods of time during C<--reindex>.

 
 Default: none, uses C<publicinbox.indexBatchSize>
 
 
 Default: none, uses C<publicinbox.indexBatchSize>