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Re: [jgit-dev] GC performance change since upgrade to 2.14
On Mon, May 29, 2017 at 2:57 PM, thomasmulhall410 via Repo and Gerrit Discussion <repo-discuss@xxxxxxxxxxxxxxxx> wrote:
Can't it be backported to 4.7?

no, it adds new API which is something we don't do in service releases
 
On Monday, May 29, 2017 at 2:01:08 AM UTC+1, David Pursehouse wrote:
On Mon, May 29, 2017 at 6:57 AM Matthias Sohn <matthi...@xxxxxxxxx> wrote:
On Fri, May 26, 2017 at 11:09 PM, Luca Milanesio <luca.mi...@xxxxxxxxx> wrote:
Hi Will,
v2.14.1 will arrive shortly: a huge number of fixes have been made on top of v2.14 (over 70).

On 26 May 2017, at 20:58, Will Saxon <sax...@xxxxxxxxx> wrote:

Hello,

We upgraded to 2.14 last weekend, and shortly afterwards started seeing a few performance issues:

- Users reported pushes would never complete (traced to autogc)

Auto-GC problem. Just disable it on JGit


That fix is going to be in JGit 4.8.0 which I don't think we'll be able to upgrade to for gerrit 2.14.x;  Instead we should mention this known issue and workaround in the release notes.
 
- Nightly 'gerrit gc' job began failing (traced to NIO2 sshd timeout)

Known issue, fixed in v2.14.1.

- Nightly builds began timing out (lack of GC)

Consequence of previous issue.


We've resolved or worked around all of the above, but the last issue we're seeing is that GC is taking 3-4x longer than with the prior version (2.13.7). We have 228 projects of varying size, and prior to the upgrade a 'gerrit gc --all' took 20-30 minutes. Now it takes ~90 minutes. Is this expected?.

Possibly question for Matthias and the JGit mailing list?

I didn't expect this, needs to be investigated.
JGit gc now moves garbage to loose objects to keep track of their timestamps individually like native git does, this could slow
down gc in case a lot of garbage has to be loosened.
 


On one of our busier projects I ran a 'gerrit gc <project> --show-progress' and it appeared to hang after the first 'Selecting commits' step. The gerrit server was using 100% of 1 CPU core at this point; running jstack several times showed that the GC thread was busy in org.eclipse.jgit.internal.storage.pack.PackWriterBitmapPreparer.setupTipCommitBitmaps. This phase of the GC took over 30 minutes by itself, after which time the rest of the expected progress output was printed.

Just wondering if there's some new configuration defaults we should look at tuning, if something is probably wrong with our installation, or if maybe this is expected because GC is doing more than it used to. It looks like there have been a lot of GC-related changes in JGit 4.6/4.7, although it's not obvious from the release notes that GC performance would be noticeably different.

Thanks,

-Will



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