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diff mercurial/revlog.py @ 34303:3c9691728237

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revlog: add option to mmap revlog index Following on from Jun Wu's patch last October[1], we have found that using mmap for the revlog index in repos with large revlogs gives a noticable performance improvment (~110ms on each hg invocation), particularly for commands that don't touch the index very much. This changeset adds this as an option, activated by a new experimental config option so that it can be enabled on a per-repo basis. The configuration option specifies an index size threshold at which Mercurial will switch to using mmap to access the index. If the configuration option is not specified, the default remains to load the full file, which seems to be the best option for smaller repos. Some initial performance numbers for average of 5 invocations of `hg log -l 5` for different cache states: | Repo: | HG | FB | |---|---|---| | Index size: | 2.3MB | much bigger | | read (warm): | 237ms | 432ms | | mmap (warm): | 227ms | 321ms | | | (-3%) | (-26%) | | read (cold): | 397ms | 696ms | | mmap (cold): | 410ms | 888ms | | | (+3%) | (+28%) | [1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-October/088737.html Test Plan: `hg log --config experimental.mmapindex=true` Differential Revision: https://phab.mercurial-scm.org/D477
author Mark Thomas <mbthomas@fb.com>
date Wed, 13 Sep 2017 17:26:26 +0000
parents 1db9abf407c5
children 7891d243d821
line wrap: on
line diff
--- a/mercurial/revlog.py	Thu Sep 21 05:54:34 2017 -0700
+++ b/mercurial/revlog.py	Wed Sep 13 17:26:26 2017 +0000
@@ -268,8 +268,13 @@
 
     If checkambig, indexfile is opened with checkambig=True at
     writing, to avoid file stat ambiguity.
+
+    If mmaplargeindex is True, and an mmapindexthreshold is set, the
+    index will be mmapped rather than read if it is larger than the
+    configured threshold.
     """
-    def __init__(self, opener, indexfile, datafile=None, checkambig=False):
+    def __init__(self, opener, indexfile, datafile=None, checkambig=False,
+                 mmaplargeindex=False):
         """
         create a revlog object
 
@@ -301,6 +306,7 @@
         self._compengine = 'zlib'
         self._maxdeltachainspan = -1
 
+        mmapindexthreshold = None
         v = REVLOG_DEFAULT_VERSION
         opts = getattr(opener, 'options', None)
         if opts is not None:
@@ -323,6 +329,8 @@
                 self._compengine = opts['compengine']
             if 'maxdeltachainspan' in opts:
                 self._maxdeltachainspan = opts['maxdeltachainspan']
+            if mmaplargeindex and 'mmapindexthreshold' in opts:
+                mmapindexthreshold = opts['mmapindexthreshold']
 
         if self._chunkcachesize <= 0:
             raise RevlogError(_('revlog chunk cache size %r is not greater '
@@ -335,7 +343,11 @@
         self._initempty = True
         try:
             f = self.opener(self.indexfile)
-            indexdata = f.read()
+            if (mmapindexthreshold is not None and
+                    self.opener.fstat(f).st_size >= mmapindexthreshold):
+                indexdata = util.buffer(util.mmapread(f))
+            else:
+                indexdata = f.read()
             f.close()
             if len(indexdata) > 0:
                 v = versionformat_unpack(indexdata[:4])[0]