# HG changeset patch
# User Paul Morelle <paul.morelle@octobus.net>
# Date 1508310468 -7200
# Node ID 8c9b08a0c48c686633e6a1bd3418d718bf14bd73
# Parent  9e18ab7f7240d768e708ba10b51e7df5864e88b8
sparse-read: skip gaps too small to be worth splitting

Splitting at too small gaps might not be worthwhile. With this changeset,
we stop considering splitting on too small gaps. The threshold is configurable.
We arbitrarily pick 256K as a default value because it seems "okay".
Further testing on various repositories and setups will be needed to tune it.

The option name is 'experimental.sparse-read.min-gap-size`, and replaces
`experimental.sparse-read.min-block-size` which is not used any more.

diff -r 9e18ab7f7240 -r 8c9b08a0c48c mercurial/configitems.py
--- a/mercurial/configitems.py	Wed Oct 18 12:53:00 2017 +0200
+++ b/mercurial/configitems.py	Wed Oct 18 09:07:48 2017 +0200
@@ -444,7 +444,7 @@
 coreconfigitem('experimental', 'sparse-read.density-threshold',
     default=0.25,
 )
-coreconfigitem('experimental', 'sparse-read.min-block-size',
+coreconfigitem('experimental', 'sparse-read.min-gap-size',
     default='256K',
 )
 coreconfigitem('experimental', 'treemanifest',
diff -r 9e18ab7f7240 -r 8c9b08a0c48c mercurial/localrepo.py
--- a/mercurial/localrepo.py	Wed Oct 18 12:53:00 2017 +0200
+++ b/mercurial/localrepo.py	Wed Oct 18 09:07:48 2017 +0200
@@ -611,11 +611,11 @@
         withsparseread = self.ui.configbool('experimental', 'sparse-read')
         srdensitythres = float(self.ui.config('experimental',
                                               'sparse-read.density-threshold'))
-        srminblocksize = self.ui.configbytes('experimental',
-                                             'sparse-read.min-block-size')
+        srmingapsize = self.ui.configbytes('experimental',
+                                           'sparse-read.min-gap-size')
         self.svfs.options['with-sparse-read'] = withsparseread
         self.svfs.options['sparse-read-density-threshold'] = srdensitythres
-        self.svfs.options['sparse-read-min-block-size'] = srminblocksize
+        self.svfs.options['sparse-read-min-gap-size'] = srmingapsize
 
         for r in self.requirements:
             if r.startswith('exp-compression-'):
diff -r 9e18ab7f7240 -r 8c9b08a0c48c mercurial/revlog.py
--- a/mercurial/revlog.py	Wed Oct 18 12:53:00 2017 +0200
+++ b/mercurial/revlog.py	Wed Oct 18 09:07:48 2017 +0200
@@ -196,7 +196,8 @@
 
         if prevend is not None:
             gapsize = revstart - prevend
-            if gapsize:
+            # only consider holes that are large enough
+            if gapsize > revlog._srmingapsize:
                 heapq.heappush(gapsheap, (-gapsize, i))
 
         prevend = revstart + revlen
@@ -371,7 +372,7 @@
         self._maxdeltachainspan = -1
         self._withsparseread = False
         self._srdensitythreshold = 0.25
-        self._srminblocksize = 262144
+        self._srmingapsize = 262144
 
         mmapindexthreshold = None
         v = REVLOG_DEFAULT_VERSION
@@ -401,8 +402,8 @@
             self._withsparseread = bool(opts.get('with-sparse-read', False))
             if 'sparse-read-density-threshold' in opts:
                 self._srdensitythreshold = opts['sparse-read-density-threshold']
-            if 'sparse-read-min-block-size' in opts:
-                self._srminblocksize = opts['sparse-read-min-block-size']
+            if 'sparse-read-min-gap-size' in opts:
+                self._srmingapsize = opts['sparse-read-min-gap-size']
 
         if self._chunkcachesize <= 0:
             raise RevlogError(_('revlog chunk cache size %r is not greater '