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