view tests/test-mq-header-date.t @ 30442:41a8106789ca

util: implement zstd compression engine

Now that zstd is vendored and being built (in some configurations), we
can implement a compression engine for zstd!

The zstd engine is a little different from existing engines. Because
it may not always be present, we have to defer load the module in case
importing it fails. We facilitate this via a cached property that holds
a reference to the module or None. The "available" method is
implemented to reflect reality.

The zstd engine declares its ability to handle bundles using the
"zstd" human name and the "ZS" internal name. The latter was chosen
because internal names are 2 characters (by only convention I think)
and "ZS" seems reasonable.

The engine, like others, supports specifying the compression level.
However, there are no consumers of this API that yet pass in that
argument. I have plans to change that, so stay tuned.

Since all we need to do to support bundle generation with a new
compression engine is implement and register the compression engine,
bundle generation with zstd "just works!" Tests demonstrating this
have been added.

How does performance of zstd for bundle generation compare? On the
mozilla-unified repo, `hg bundle --all -t <engine>-v2` yields the
following on my i7-6700K on Linux:

engine        CPU time     bundle size   vs orig size   throughput
none            97.0s     4,054,405,584     100.0%       41.8 MB/s
bzip2 (l=9)    393.6s       975,343,098      24.0%       10.3 MB/s
gzip (l=6)     184.0s     1,140,533,074      28.1%       22.0 MB/s
zstd (l=1)     108.2s     1,119,434,718      27.6%       37.5 MB/s
zstd (l=2)     111.3s     1,078,328,002      26.6%       36.4 MB/s
zstd (l=3)     113.7s     1,011,823,727      25.0%       35.7 MB/s
zstd (l=4)     116.0s     1,008,965,888      24.9%       35.0 MB/s
zstd (l=5)     121.0s       977,203,148      24.1%       33.5 MB/s
zstd (l=6)     131.7s       927,360,198      22.9%       30.8 MB/s
zstd (l=7)     139.0s       912,808,505      22.5%       29.2 MB/s
zstd (l=12)    198.1s       854,527,714      21.1%       20.5 MB/s
zstd (l=18)    681.6s       789,750,690      19.5%        5.9 MB/s

On compression, zstd for bundle generation delivers:

* better compression than gzip with significantly less CPU utilization
* better than bzip2 compression ratios while still being significantly
  faster than gzip
* ability to aggressively tune compression level to achieve
  significantly smaller bundles

That last point is important. With clone bundles, a server can
pre-generate a bundle file, upload it to a static file server, and
redirect clients to transparently download it during clone. The server
could choose to produce a zstd bundle with the highest compression
settings possible. This would take a very long time - a magnitude
longer than a typical zstd bundle generation - but the result would
be hundreds of megabytes smaller! For the clone volume we do at
Mozilla, this could translate to petabytes of bandwidth savings
per year and faster clones (due to smaller transfer size).

I don't have detailed numbers to report on decompression. However,
zstd decompression is fast: >1 GB/s output throughput on this machine,
even through the Python bindings. And it can do that regardless of the
compression level of the input. By the time you have enough data to
worry about overhead of decompression, you have plenty of other things
to worry about performance wise.

zstd is wins all around. I can't wait to implement support for it
on the wire protocol and in revlogs.

  $ cat <<EOF >> $HGRCPATH
  > [extensions]
  > mq =
  > [diff]
  > nodates = true
  > EOF
  $ catpatch() {
  >     cat .hg/patches/$1.patch | sed -e "s/^diff \-r [0-9a-f]* /diff -r ... /" \
  >                                    -e "s/^\(# Parent \).*/\1/"
  > }
  $ catlog() {
  >     catpatch $1
  >     hg log --template "{rev}: {desc} - {author}\n"
  > }
  $ catlogd() {
  >     catpatch $1
  >     hg log --template "{rev}: {desc} - {author} - {date}\n"
  > }
  $ drop() {
  >     hg qpop
  >     hg qdel $1.patch
  > }
  $ runtest() {
  >     echo ==== init
  >     hg init a
  >     cd a
  >     hg qinit
  > 
  > 
  >     echo ==== qnew -d
  >     hg qnew -d '3 0' 1.patch
  >     catlogd 1
  > 
  >     echo ==== qref
  >     echo "1" >1
  >     hg add
  >     hg qref
  >     catlogd 1
  > 
  >     echo ==== qref -d
  >     hg qref -d '4 0'
  >     catlogd 1
  > 
  > 
  >     echo ==== qnew
  >     hg qnew 2.patch
  >     echo "2" >2
  >     hg add
  >     hg qref
  >     catlog 2
  > 
  >     echo ==== qref -d
  >     hg qref -d '5 0'
  >     catlog 2
  > 
  >     drop 2
  > 
  > 
  >     echo ==== qnew -d -m
  >     hg qnew -d '6 0' -m "Three" 3.patch
  >     catlogd 3
  > 
  >     echo ==== qref
  >     echo "3" >3
  >     hg add
  >     hg qref
  >     catlogd 3
  > 
  >     echo ==== qref -m
  >     hg qref -m "Drei"
  >     catlogd 3
  > 
  >     echo ==== qref -d
  >     hg qref -d '7 0'
  >     catlogd 3
  > 
  >     echo ==== qref -d -m
  >     hg qref -d '8 0' -m "Three (again)"
  >     catlogd 3
  > 
  > 
  >     echo ==== qnew -m
  >     hg qnew -m "Four" 4.patch
  >     echo "4" >4
  >     hg add
  >     hg qref
  >     catlog 4
  > 
  >     echo ==== qref -d
  >     hg qref -d '9 0'
  >     catlog 4
  > 
  >     drop 4
  > 
  > 
  >     echo ==== qnew with HG header
  >     hg qnew --config 'mq.plain=true' 5.patch
  >     hg qpop
  >     echo "# HG changeset patch" >>.hg/patches/5.patch
  >     echo "# Date 10 0" >>.hg/patches/5.patch
  >     hg qpush 2>&1 | grep 'Now at'
  >     catlogd 5
  > 
  >     echo ==== hg qref
  >     echo "5" >5
  >     hg add
  >     hg qref
  >     catlogd 5
  > 
  >     echo ==== hg qref -d
  >     hg qref -d '11 0'
  >     catlogd 5
  > 
  > 
  >     echo ==== qnew with plain header
  >     hg qnew --config 'mq.plain=true' -d '12 0' 6.patch
  >     hg qpop
  >     hg qpush 2>&1 | grep 'now at'
  >     catlog 6
  > 
  >     echo ==== hg qref
  >     echo "6" >6
  >     hg add
  >     hg qref
  >     catlogd 6
  > 
  >     echo ==== hg qref -d
  >     hg qref -d '13 0'
  >     catlogd 6
  > 
  >     drop 6
  > 
  > 
  >     echo ==== qnew -u
  >     hg qnew -u jane 6.patch
  >     echo "6" >6
  >     hg add
  >     hg qref
  >     catlog 6
  > 
  >     echo ==== qref -d
  >     hg qref -d '12 0'
  >     catlog 6
  > 
  >     drop 6
  > 
  > 
  >     echo ==== qnew -d
  >     hg qnew -d '13 0' 7.patch
  >     echo "7" >7
  >     hg add
  >     hg qref
  >     catlog 7
  > 
  >     echo ==== qref -u
  >     hg qref -u john
  >     catlogd 7
  > 
  > 
  >     echo ==== qnew
  >     hg qnew 8.patch
  >     echo "8" >8
  >     hg add
  >     hg qref
  >     catlog 8
  > 
  >     echo ==== qref -u -d
  >     hg qref -u john -d '14 0'
  >     catlog 8
  > 
  >     drop 8
  > 
  > 
  >     echo ==== qnew -m
  >     hg qnew -m "Nine" 9.patch
  >     echo "9" >9
  >     hg add
  >     hg qref
  >     catlog 9
  > 
  >     echo ==== qref -u -d
  >     hg qref -u john -d '15 0'
  >     catlog 9
  > 
  >     drop 9
  > 
  > 
  >     echo ==== "qpop -a / qpush -a"
  >     hg qpop -a
  >     hg qpush -a
  >     hg log --template "{rev}: {desc} - {author} - {date}\n"
  > }

======= plain headers

  $ echo "[mq]" >> $HGRCPATH
  $ echo "plain=true" >> $HGRCPATH
  $ mkdir sandbox
  $ (cd sandbox ; runtest)
  ==== init
  ==== qnew -d
  Date: 3 0
  
  0: [mq]: 1.patch - test - 3.00
  ==== qref
  adding 1
  Date: 3 0
  
  diff -r ... 1
  --- /dev/null
  +++ b/1
  @@ -0,0 +1,1 @@
  +1
  0: [mq]: 1.patch - test - 3.00
  ==== qref -d
  Date: 4 0
  
  diff -r ... 1
  --- /dev/null
  +++ b/1
  @@ -0,0 +1,1 @@
  +1
  0: [mq]: 1.patch - test - 4.00
  ==== qnew
  adding 2
  diff -r ... 2
  --- /dev/null
  +++ b/2
  @@ -0,0 +1,1 @@
  +2
  1: [mq]: 2.patch - test
  0: [mq]: 1.patch - test
  ==== qref -d
  Date: 5 0
  
  diff -r ... 2
  --- /dev/null
  +++ b/2
  @@ -0,0 +1,1 @@
  +2
  1: [mq]: 2.patch - test
  0: [mq]: 1.patch - test
  popping 2.patch
  now at: 1.patch
  ==== qnew -d -m
  Date: 6 0
  
  Three
  
  1: Three - test - 6.00
  0: [mq]: 1.patch - test - 4.00
  ==== qref
  adding 3
  Date: 6 0
  
  Three
  
  diff -r ... 3
  --- /dev/null
  +++ b/3
  @@ -0,0 +1,1 @@
  +3
  1: Three - test - 6.00
  0: [mq]: 1.patch - test - 4.00
  ==== qref -m
  Date: 6 0
  
  Drei
  
  diff -r ... 3
  --- /dev/null
  +++ b/3
  @@ -0,0 +1,1 @@
  +3
  1: Drei - test - 6.00
  0: [mq]: 1.patch - test - 4.00
  ==== qref -d
  Date: 7 0
  
  Drei
  
  diff -r ... 3
  --- /dev/null
  +++ b/3
  @@ -0,0 +1,1 @@
  +3
  1: Drei - test - 7.00
  0: [mq]: 1.patch - test - 4.00
  ==== qref -d -m
  Date: 8 0
  
  Three (again)
  
  diff -r ... 3
  --- /dev/null
  +++ b/3
  @@ -0,0 +1,1 @@
  +3
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  ==== qnew -m
  adding 4
  Four
  
  diff -r ... 4
  --- /dev/null
  +++ b/4
  @@ -0,0 +1,1 @@
  +4
  2: Four - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  ==== qref -d
  Date: 9 0
  
  Four
  
  diff -r ... 4
  --- /dev/null
  +++ b/4
  @@ -0,0 +1,1 @@
  +4
  2: Four - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  popping 4.patch
  now at: 3.patch
  ==== qnew with HG header
  popping 5.patch
  now at: 3.patch
  # HG changeset patch
  # Date 10 0
  2: imported patch 5.patch - test - 10.00
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  ==== hg qref
  adding 5
  # HG changeset patch
  # Date 10 0
  # Parent 
  
  diff -r ... 5
  --- /dev/null
  +++ b/5
  @@ -0,0 +1,1 @@
  +5
  2: [mq]: 5.patch - test - 10.00
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  ==== hg qref -d
  # HG changeset patch
  # Date 11 0
  # Parent 
  
  diff -r ... 5
  --- /dev/null
  +++ b/5
  @@ -0,0 +1,1 @@
  +5
  2: [mq]: 5.patch - test - 11.00
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  ==== qnew with plain header
  popping 6.patch
  now at: 5.patch
  now at: 6.patch
  Date: 12 0
  
  3: imported patch 6.patch - test
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  ==== hg qref
  adding 6
  Date: 12 0
  
  diff -r ... 6
  --- /dev/null
  +++ b/6
  @@ -0,0 +1,1 @@
  +6
  3: [mq]: 6.patch - test - 12.00
  2: [mq]: 5.patch - test - 11.00
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  ==== hg qref -d
  Date: 13 0
  
  diff -r ... 6
  --- /dev/null
  +++ b/6
  @@ -0,0 +1,1 @@
  +6
  3: [mq]: 6.patch - test - 13.00
  2: [mq]: 5.patch - test - 11.00
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  popping 6.patch
  now at: 5.patch
  ==== qnew -u
  adding 6
  From: jane
  
  diff -r ... 6
  --- /dev/null
  +++ b/6
  @@ -0,0 +1,1 @@
  +6
  3: [mq]: 6.patch - jane
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  ==== qref -d
  From: jane
  Date: 12 0
  
  diff -r ... 6
  --- /dev/null
  +++ b/6
  @@ -0,0 +1,1 @@
  +6
  3: [mq]: 6.patch - jane
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  popping 6.patch
  now at: 5.patch
  ==== qnew -d
  adding 7
  Date: 13 0
  
  diff -r ... 7
  --- /dev/null
  +++ b/7
  @@ -0,0 +1,1 @@
  +7
  3: [mq]: 7.patch - test
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  ==== qref -u
  From: john
  Date: 13 0
  
  diff -r ... 7
  --- /dev/null
  +++ b/7
  @@ -0,0 +1,1 @@
  +7
  3: [mq]: 7.patch - john - 13.00
  2: [mq]: 5.patch - test - 11.00
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  ==== qnew
  adding 8
  diff -r ... 8
  --- /dev/null
  +++ b/8
  @@ -0,0 +1,1 @@
  +8
  4: [mq]: 8.patch - test
  3: [mq]: 7.patch - john
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  ==== qref -u -d
  From: john
  Date: 14 0
  
  diff -r ... 8
  --- /dev/null
  +++ b/8
  @@ -0,0 +1,1 @@
  +8
  4: [mq]: 8.patch - john
  3: [mq]: 7.patch - john
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  popping 8.patch
  now at: 7.patch
  ==== qnew -m
  adding 9
  Nine
  
  diff -r ... 9
  --- /dev/null
  +++ b/9
  @@ -0,0 +1,1 @@
  +9
  4: Nine - test
  3: [mq]: 7.patch - john
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  ==== qref -u -d
  From: john
  Date: 15 0
  
  Nine
  
  diff -r ... 9
  --- /dev/null
  +++ b/9
  @@ -0,0 +1,1 @@
  +9
  4: Nine - john
  3: [mq]: 7.patch - john
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  popping 9.patch
  now at: 7.patch
  ==== qpop -a / qpush -a
  popping 7.patch
  popping 5.patch
  popping 3.patch
  popping 1.patch
  patch queue now empty
  applying 1.patch
  applying 3.patch
  applying 5.patch
  applying 7.patch
  now at: 7.patch
  3: imported patch 7.patch - john - 13.00
  2: imported patch 5.patch - test - 11.00
  1: Three (again) - test - 8.00
  0: imported patch 1.patch - test - 4.00
  $ rm -r sandbox

======= hg headers

  $ echo "plain=false" >> $HGRCPATH
  $ mkdir sandbox
  $ (cd sandbox ; runtest)
  ==== init
  ==== qnew -d
  # HG changeset patch
  # Date 3 0
  # Parent 
  
  0: [mq]: 1.patch - test - 3.00
  ==== qref
  adding 1
  # HG changeset patch
  # Date 3 0
  # Parent 
  
  diff -r ... 1
  --- /dev/null
  +++ b/1
  @@ -0,0 +1,1 @@
  +1
  0: [mq]: 1.patch - test - 3.00
  ==== qref -d
  # HG changeset patch
  # Date 4 0
  # Parent 
  
  diff -r ... 1
  --- /dev/null
  +++ b/1
  @@ -0,0 +1,1 @@
  +1
  0: [mq]: 1.patch - test - 4.00
  ==== qnew
  adding 2
  # HG changeset patch
  # Parent 
  
  diff -r ... 2
  --- /dev/null
  +++ b/2
  @@ -0,0 +1,1 @@
  +2
  1: [mq]: 2.patch - test
  0: [mq]: 1.patch - test
  ==== qref -d
  # HG changeset patch
  # Date 5 0
  # Parent 
  
  diff -r ... 2
  --- /dev/null
  +++ b/2
  @@ -0,0 +1,1 @@
  +2
  1: [mq]: 2.patch - test
  0: [mq]: 1.patch - test
  popping 2.patch
  now at: 1.patch
  ==== qnew -d -m
  # HG changeset patch
  # Date 6 0
  # Parent 
  Three
  
  1: Three - test - 6.00
  0: [mq]: 1.patch - test - 4.00
  ==== qref
  adding 3
  # HG changeset patch
  # Date 6 0
  # Parent 
  Three
  
  diff -r ... 3
  --- /dev/null
  +++ b/3
  @@ -0,0 +1,1 @@
  +3
  1: Three - test - 6.00
  0: [mq]: 1.patch - test - 4.00
  ==== qref -m
  # HG changeset patch
  # Date 6 0
  # Parent 
  Drei
  
  diff -r ... 3
  --- /dev/null
  +++ b/3
  @@ -0,0 +1,1 @@
  +3
  1: Drei - test - 6.00
  0: [mq]: 1.patch - test - 4.00
  ==== qref -d
  # HG changeset patch
  # Date 7 0
  # Parent 
  Drei
  
  diff -r ... 3
  --- /dev/null
  +++ b/3
  @@ -0,0 +1,1 @@
  +3
  1: Drei - test - 7.00
  0: [mq]: 1.patch - test - 4.00
  ==== qref -d -m
  # HG changeset patch
  # Date 8 0
  # Parent 
  Three (again)
  
  diff -r ... 3
  --- /dev/null
  +++ b/3
  @@ -0,0 +1,1 @@
  +3
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  ==== qnew -m
  adding 4
  # HG changeset patch
  # Parent 
  Four
  
  diff -r ... 4
  --- /dev/null
  +++ b/4
  @@ -0,0 +1,1 @@
  +4
  2: Four - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  ==== qref -d
  # HG changeset patch
  # Date 9 0
  # Parent 
  Four
  
  diff -r ... 4
  --- /dev/null
  +++ b/4
  @@ -0,0 +1,1 @@
  +4
  2: Four - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  popping 4.patch
  now at: 3.patch
  ==== qnew with HG header
  popping 5.patch
  now at: 3.patch
  # HG changeset patch
  # Date 10 0
  2: imported patch 5.patch - test - 10.00
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  ==== hg qref
  adding 5
  # HG changeset patch
  # Date 10 0
  # Parent 
  
  diff -r ... 5
  --- /dev/null
  +++ b/5
  @@ -0,0 +1,1 @@
  +5
  2: [mq]: 5.patch - test - 10.00
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  ==== hg qref -d
  # HG changeset patch
  # Date 11 0
  # Parent 
  
  diff -r ... 5
  --- /dev/null
  +++ b/5
  @@ -0,0 +1,1 @@
  +5
  2: [mq]: 5.patch - test - 11.00
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  ==== qnew with plain header
  popping 6.patch
  now at: 5.patch
  now at: 6.patch
  Date: 12 0
  
  3: imported patch 6.patch - test
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  ==== hg qref
  adding 6
  Date: 12 0
  
  diff -r ... 6
  --- /dev/null
  +++ b/6
  @@ -0,0 +1,1 @@
  +6
  3: [mq]: 6.patch - test - 12.00
  2: [mq]: 5.patch - test - 11.00
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  ==== hg qref -d
  Date: 13 0
  
  diff -r ... 6
  --- /dev/null
  +++ b/6
  @@ -0,0 +1,1 @@
  +6
  3: [mq]: 6.patch - test - 13.00
  2: [mq]: 5.patch - test - 11.00
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  popping 6.patch
  now at: 5.patch
  ==== qnew -u
  adding 6
  # HG changeset patch
  # User jane
  # Parent 
  
  diff -r ... 6
  --- /dev/null
  +++ b/6
  @@ -0,0 +1,1 @@
  +6
  3: [mq]: 6.patch - jane
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  ==== qref -d
  # HG changeset patch
  # User jane
  # Date 12 0
  # Parent 
  
  diff -r ... 6
  --- /dev/null
  +++ b/6
  @@ -0,0 +1,1 @@
  +6
  3: [mq]: 6.patch - jane
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  popping 6.patch
  now at: 5.patch
  ==== qnew -d
  adding 7
  # HG changeset patch
  # Date 13 0
  # Parent 
  
  diff -r ... 7
  --- /dev/null
  +++ b/7
  @@ -0,0 +1,1 @@
  +7
  3: [mq]: 7.patch - test
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  ==== qref -u
  # HG changeset patch
  # User john
  # Date 13 0
  # Parent 
  
  diff -r ... 7
  --- /dev/null
  +++ b/7
  @@ -0,0 +1,1 @@
  +7
  3: [mq]: 7.patch - john - 13.00
  2: [mq]: 5.patch - test - 11.00
  1: Three (again) - test - 8.00
  0: [mq]: 1.patch - test - 4.00
  ==== qnew
  adding 8
  # HG changeset patch
  # Parent 
  
  diff -r ... 8
  --- /dev/null
  +++ b/8
  @@ -0,0 +1,1 @@
  +8
  4: [mq]: 8.patch - test
  3: [mq]: 7.patch - john
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  ==== qref -u -d
  # HG changeset patch
  # User john
  # Date 14 0
  # Parent 
  
  diff -r ... 8
  --- /dev/null
  +++ b/8
  @@ -0,0 +1,1 @@
  +8
  4: [mq]: 8.patch - john
  3: [mq]: 7.patch - john
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  popping 8.patch
  now at: 7.patch
  ==== qnew -m
  adding 9
  # HG changeset patch
  # Parent 
  Nine
  
  diff -r ... 9
  --- /dev/null
  +++ b/9
  @@ -0,0 +1,1 @@
  +9
  4: Nine - test
  3: [mq]: 7.patch - john
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  ==== qref -u -d
  # HG changeset patch
  # User john
  # Date 15 0
  # Parent 
  Nine
  
  diff -r ... 9
  --- /dev/null
  +++ b/9
  @@ -0,0 +1,1 @@
  +9
  4: Nine - john
  3: [mq]: 7.patch - john
  2: [mq]: 5.patch - test
  1: Three (again) - test
  0: [mq]: 1.patch - test
  popping 9.patch
  now at: 7.patch
  ==== qpop -a / qpush -a
  popping 7.patch
  popping 5.patch
  popping 3.patch
  popping 1.patch
  patch queue now empty
  applying 1.patch
  applying 3.patch
  applying 5.patch
  applying 7.patch
  now at: 7.patch
  3: imported patch 7.patch - john - 13.00
  2: imported patch 5.patch - test - 11.00
  1: Three (again) - test - 8.00
  0: imported patch 1.patch - test - 4.00
  $ rm -r sandbox