# HG changeset patch
# User Gregory Szorc <gregory.szorc@gmail.com>
# Date 2015-12-06 07:37:46
# Node ID 4efb36ecaaec058db222f0286ce276111f31e47c
# Parent 3d0feb2f978b040be05cfde635eb11b3baadf287
commands: add debugdeltachain command
We have debug commands for displaying overall revlog statistics
(debugrevlog) and for dumping a revlog index (debugindex). As part
of investigating various aspects of revlog behavior and performance,
I found it important to have an understanding of how revlog
delta chains behave in practice.
This patch implements a "debugdeltachain" command. For each revision
in a revlog, it dumps information about the delta chain. Which delta
chain it is part of, length of the delta chain, distance since base
revision, info about base revision, size of the delta chain, etc. The
generic formatting facility is used, which means we can templatize
output and get machine readable output like JSON.
This command has already uncovered some weird history in
mozilla-central I didn't know about. So I think it's valuable.
diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -2501,6 +2501,117 @@ def debugindexdot(ui, repo, file_=None,
ui.write("\t%d -> %d\n" % (r.rev(pp[1]), i))
ui.write("}\n")
+@command('debugdeltachain',
+ debugrevlogopts + formatteropts,
+ _('-c|-m|FILE'),
+ optionalrepo=True)
+def debugdeltachain(ui, repo, file_=None, **opts):
+ """dump information about delta chains in a revlog
+
+ Output can be templatized. Available template keywords are:
+
+ rev revision number
+ chainid delta chain identifier (numbered by unique base)
+ chainlen delta chain length to this revision
+ prevrev previous revision in delta chain
+ deltatype role of delta / how it was computed
+ compsize compressed size of revision
+ uncompsize uncompressed size of revision
+ chainsize total size of compressed revisions in chain
+ chainratio total chain size divided by uncompressed revision size
+ (new delta chains typically start at ratio 2.00)
+ lindist linear distance from base revision in delta chain to end
+ of this revision
+ extradist total size of revisions not part of this delta chain from
+ base of delta chain to end of this revision; a measurement
+ of how much extra data we need to read/seek across to read
+ the delta chain for this revision
+ extraratio extradist divided by chainsize; another representation of
+ how much unrelated data is needed to load this delta chain
+ """
+ r = cmdutil.openrevlog(repo, 'debugdeltachain', file_, opts)
+ index = r.index
+ generaldelta = r.version & revlog.REVLOGGENERALDELTA
+
+ def revinfo(rev):
+ iterrev = rev
+ e = index[iterrev]
+ chain = []
+ compsize = e[1]
+ uncompsize = e[2]
+ chainsize = 0
+
+ if generaldelta:
+ if e[3] == e[5]:
+ deltatype = 'p1'
+ elif e[3] == e[6]:
+ deltatype = 'p2'
+ elif e[3] == rev - 1:
+ deltatype = 'prev'
+ elif e[3] == rev:
+ deltatype = 'base'
+ else:
+ deltatype = 'other'
+ else:
+ if e[3] == rev:
+ deltatype = 'base'
+ else:
+ deltatype = 'prev'
+
+ while iterrev != e[3]:
+ chain.append(iterrev)
+ chainsize += e[1]
+ if generaldelta:
+ iterrev = e[3]
+ else:
+ iterrev -= 1
+ e = index[iterrev]
+ else:
+ chainsize += e[1]
+ chain.append(iterrev)
+
+ chain.reverse()
+ return compsize, uncompsize, deltatype, chain, chainsize
+
+ fm = ui.formatter('debugdeltachain', opts)
+
+ fm.plain(' rev chain# chainlen prev delta '
+ 'size rawsize chainsize ratio lindist extradist '
+ 'extraratio\n')
+
+ chainbases = {}
+ for rev in r:
+ comp, uncomp, deltatype, chain, chainsize = revinfo(rev)
+ chainbase = chain[0]
+ chainid = chainbases.setdefault(chainbase, len(chainbases) + 1)
+ basestart = r.start(chainbase)
+ revstart = r.start(rev)
+ lineardist = revstart + comp - basestart
+ extradist = lineardist - chainsize
+ try:
+ prevrev = chain[-2]
+ except IndexError:
+ prevrev = -1
+
+ chainratio = float(chainsize) / float(uncomp)
+ extraratio = float(extradist) / float(chainsize)
+
+ fm.startitem()
+ fm.write('rev chainid chainlen prevrev deltatype compsize '
+ 'uncompsize chainsize chainratio lindist extradist '
+ 'extraratio',
+ '%7d %7d %8d %8d %7s %10d %10d %10d %9.5f %9d %9d %10.5f\n',
+ rev, chainid, len(chain), prevrev, deltatype, comp,
+ uncomp, chainsize, chainratio, lineardist, extradist,
+ extraratio,
+ rev=rev, chainid=chainid, chainlen=len(chain),
+ prevrev=prevrev, deltatype=deltatype, compsize=comp,
+ uncompsize=uncomp, chainsize=chainsize,
+ chainratio=chainratio, lindist=lineardist,
+ extradist=extradist, extraratio=extraratio)
+
+ fm.end()
+
@command('debuginstall', [], '', norepo=True)
def debuginstall(ui):
'''test Mercurial installation
diff --git a/tests/test-completion.t b/tests/test-completion.t
--- a/tests/test-completion.t
+++ b/tests/test-completion.t
@@ -80,6 +80,7 @@ Show debug commands if there are no othe
debugdag
debugdata
debugdate
+ debugdeltachain
debugdirstate
debugdiscovery
debugextensions
@@ -243,6 +244,7 @@ Show all commands + options
debugdag: tags, branches, dots, spaces
debugdata: changelog, manifest, dir
debugdate: extended
+ debugdeltachain: changelog, manifest, dir, template
debugdirstate: nodates, datesort
debugdiscovery: old, nonheads, ssh, remotecmd, insecure
debugextensions: template
diff --git a/tests/test-debugcommands.t b/tests/test-debugcommands.t
--- a/tests/test-debugcommands.t
+++ b/tests/test-debugcommands.t
@@ -44,6 +44,32 @@ Test debugindex, with and without the --
rev flag offset length size ..... link p1 p2 nodeid (re)
0 0000 0 3 2 .... 0 -1 -1 b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 (re)
+debugdelta chain basic output
+
+ $ hg debugdeltachain -m
+ rev chain# chainlen prev delta size rawsize chainsize ratio lindist extradist extraratio
+ 0 1 1 -1 base 44 43 44 1.02326 44 0 0.00000
+
+ $ hg debugdeltachain -m -T '{rev} {chainid} {chainlen}\n'
+ 0 1 1
+
+ $ hg debugdeltachain -m -Tjson
+ [
+ {
+ "chainid": 1,
+ "chainlen": 1,
+ "chainratio": 1.02325581395,
+ "chainsize": 44,
+ "compsize": 44,
+ "deltatype": "base",
+ "extradist": 0,
+ "extraratio": 0.0,
+ "lindist": 44,
+ "prevrev": -1,
+ "rev": 0,
+ "uncompsize": 43
+ }
+ ]
Test max chain len
$ cat >> $HGRCPATH << EOF
diff --git a/tests/test-help.t b/tests/test-help.t
--- a/tests/test-help.t
+++ b/tests/test-help.t
@@ -812,6 +812,8 @@ Test list of internal help commands
description
debugdata dump the contents of a data file revision
debugdate parse and display a date
+ debugdeltachain
+ dump information about delta chains in a revlog
debugdirstate
show the contents of the current dirstate
debugdiscovery