Canonical Voices

Posts tagged with 'speed'

Martin gz

Last week was the Bazaar sprint, which was fantastic and tiring. Somehow even the people who’d been at UDS just before made it through five packed days of fixing bugs, preparing releases, and debugging package imports. We were most hospitably hosted at the Canonical offices a long way up Millbank tower. But even those who couldn’t be there in person to enjoy the view were part of the experience. At home in the Ukraine Alexander wore his Bazaar shirt in support during the first day. On IRC larstiq and santagada ran the test suite on pypy and investigated incompatibilities. And all week we had a small robot John sitting in the middle of the table on the line from the Netherlands, working on performance bugs and offering helpful advice.

There were two new faces introduced. Max has been a stalwart maintaining the ~bzr PPAs and getting daily builds working. Jonathan is joining the Bazaar team on rotation from Kubuntu, which is very exciting for fans of qbzr. He started getting to know bzrlib by taking on some bugs tagged ‘easy’ and pair programming on harder ones. It was a bit tough to keep track of everything going on, but good progress was made on the Ubuntu Distributed Development front, the translation framework branches Naoki put together were landed, and lots of pet bugs were fixed. Download bzr 2.4b3 now to see the rest of the results for yourself.

After these long days in front of screens a nice meal out was a welcome treat. Over dinner we even managed to get on to topics other than code on occasion. On Thursday evening everyone went to As You Like It at the Globe as groundlings. Even with the language barrier to overcome for some of the sprinters, the comedy lived up to the categorisation. Trying to use the cycle hire scheme to travel there and back proved more of an obstacle. The bikes themselves were fine, provided you could get past the terrible computer interface and persuade the system to let you rent them. Now, if only they took patches for that…

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jameinel

The last of my patches is queued up to land, so I figured I’d post an update about the performance improvements I’ve been working on. I’m also just excited about how well it has all come together.

There were essentially 3 changes that mattered for performance on large trees.

  1. Fixing iter_entries_by_dir() to preload the data in Repository- optimal ordering rather than by-request ordering. In large trees this was causing us to thrash and become pathologically slow. In the 70,000-file test tree, thrashing took about 3 minutes, the preloading version takes about 15s. This affected a lot of our commands, though I guess the next two fixes would actually reduce the number of commands affected by this.
  2. Fixing several code paths to use optimized iter_changes() rather than the generic iter_changes(). The generic path walks both inventories iter_entries_by_dir() and compares them. Our 2a format Repository can do iter_changes without loading the whole tree. (It internally uses a hash_trie to store the inventory, and so nodes with matching sub-trees can be skipped for comparison.) This generally shows up as something that was taking 15s (to load the whole inventory) dropping to <2s for the improved comparison. (bzr revert and bzr pull were both directly impacted here)
  3. Changing WT.set_parent_trees([one_tree]) to update itself using current_basis.iter_changes(one_tree), rather than setting the state from scratch. This basically adds another case where we can avoid reading the whole inventory state again, which is another 15s to <2s sort of change. This only showed up after fixing (2), because once the tree is loaded, the other actions are generally pretty quick. (bzr up, bzr pull)

This is the chart I put together for “whats-new-in-2.4.txt”. bzr-2.3.2 will have fix (1), but not (2) or (3), to give a feel for how much of an impact different fixes have had.

    bzr-2.3.1 bzr-2.3.2 bzr-2.4  action
    3m39s         1m08s   1m03s  bzr co --lightweight
      38s            8s      2s  bzr revert (in a clean tree)
    4m47s         3m56s     15s  bzr merge
    4m45s           20s      3s  bzr pull
    4m58s         3m00s      2s  bzr up
    9m33s           21s     19s  bzr uncommit (including a merge)
    4m44s           17s      2s  bzr uncommit (simple commit)

So yes, some operations that were taking almost 5 minutes have now dropped down to taking <3s.

You won’t see that dramatic of an improvement for smaller trees, though most cases will have a pleasant improvement. Here is a short list for the ‘Launchpad‘ tree (with ~8k items).

    bzr-2.3.1   bzr-2.4     action
    5.3s        5.2s        bzr co --lightweight
    0.9s        0.3s        bzr revert
    1.4s        0.4s        bzr pull
    3.9s        3.7s        bzr uncommit (with merge)
    0.9s        0.3s        bzr uncommit (without merge)

Anyway, I’m quite happy about how much better bzr-2.4 will be in large trees.

update:Add graphs…

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Martin Pool

Parth announced bzr-grep 0.2.0.  Amongst other things there are performance enhancements such that Eli says:

Thanks, this looks great. I just tried it on Windows XP searching for a fixed string in the Emacs repository — took 28 seconds with a cold cache and only 7.5 with a warm cache, which is impressive.

By contrast, “grep -F -R” (with suitable –exclude patterns, to prevent it from searching binary files and inside .bzr) took about 12.5 seconds with a warm cache.


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Ian Clatworthy


Are you a Bazaar fan and need some help explaining to others why Bazaar is cool? I published a document last week called Why switch to Bazaar? that may help. I’ve tried hard to present the big picture together with some concrete examples, explaining what we stand for and what that means to users, teams and communities in reality. Furthermore, if you tried Bazaar 1.x but found it too slow or inefficient, I’m sure you’ll find the Bazaar 2.0 benchmarks included in the document great news.

I hope you find the document interesting and food for thought. If there are any mistakes or you’ll like to translate the document to another language, please let me know.

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