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Zuul references cleaner

Zuul mergers create a vast number of git references under /refs/zuul
which are never garbage collected.

With hundred of thousands of references, that makes git fetch operations
very slow since git uploads all references to Gerrit to synchronize the
Zuul maintained repository.  On one of Wikimedia busy repository
(mediawiki/core) we had 55000 such references and it can take up to 18
seconds for a fetch to complete.  I have seen occurences of a merge
taking 2 minutes to complete.

As such, this tiny script clears out references for which the commit date
of the pointed commit object is older than 360 days (the default).

It is not perfect since a recent reference can well point to an old
object.  That would be the case on repositories that are barely active.
In such case the ref will be gone despite it being recently created.

A better way would be to vary Zuul references by using month/day which
will let one easily garbage collect them.  But I am being lazy and that
would not let us clear out references using the current scheme.

Example usage:

 zuul-clear-refs.py --verbose --dry-run --until 90 /srv/zuul/git/project

Would show a list of references pointing to commit dates older than 90
days and output a message whenever the script would delete them.

Hint about the utility in our merger documentation.

Reference:
 https://phabricator.wikimedia.org/T70481

Change-Id: Id4e55f5d571ebd5e8271e516f53f8e05c1f78c1a
changes/76/109276/9
Antoine Musso 7 years ago
parent
commit
d9ac4c18b1
2 changed files with 108 additions and 0 deletions
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      doc/source/merger.rst
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      tools/zuul-clear-refs.py

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@ -58,3 +58,17 @@ instance, a clone will produce a repository in an unpredictable state
depending on what the state of Zuul's repository is when the clone
happens). They are, however, suitable for automated systems that
respond to Zuul triggers.
Clearing old references
~~~~~~~~~~~~~~~~~~~~~~~
The references created under refs/zuul are not garbage collected. Since
git fetch send them all to Gerrit to sync the repositories, the time
spent on merge will slightly grow overtime and start being noticeable.
To clean them you can use the ``tools/zuul-clear-refs.py`` script on
each repositories. It will delete Zuul references that point to commits
for which the commit date is older than a given amount of days (default
360)::
./tools/zuul-clear-refs.py /path/to/zuul/git/repo

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tools/zuul-clear-refs.py View File

@ -0,0 +1,94 @@
#!/usr/bin/env python
# Copyright 2014-2015 Antoine "hashar" Musso
# Copyright 2014-2015 Wikimedia Foundation Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
# pylint: disable=locally-disabled, invalid-name
"""
Zuul references cleaner.
Clear up references under /refs/zuul/ by inspecting the age of the commit the
reference points to. If the commit date is older than a number of days
specificed by --until, the reference is deleted from the git repository.
Use --dry-run --verbose to finely inspect the script behavior.
"""
import argparse
import git
import logging
import time
import sys
NOW = int(time.time())
DEFAULT_DAYS = 360
ZUUL_REF_PREFIX = 'refs/zuul/'
parser = argparse.ArgumentParser(
description=__doc__,
formatter_class=argparse.RawDescriptionHelpFormatter,
)
parser.add_argument('--until', dest='days_ago', default=DEFAULT_DAYS, type=int,
help='references older than this number of day will '
'be deleted. Default: %s' % DEFAULT_DAYS)
parser.add_argument('-n', '--dry-run', dest='dryrun', action='store_true',
help='do not delete references')
parser.add_argument('-v', '--verbose', dest='verbose', action='store_true',
help='set log level from info to debug')
parser.add_argument('gitrepo', help='path to a Zuul git repository')
args = parser.parse_args()
logging.basicConfig()
log = logging.getLogger('zuul-clear-refs')
if args.verbose:
log.setLevel(logging.DEBUG)
else:
log.setLevel(logging.INFO)
try:
repo = git.Repo(args.gitrepo)
except git.exc.InvalidGitRepositoryError:
log.error("Invalid git repo: %s" % args.gitrepo)
sys.exit(1)
for ref in repo.references:
if not ref.path.startswith(ZUUL_REF_PREFIX):
continue
if type(ref) is not git.refs.reference.Reference:
# Paranoia: ignore heads/tags/remotes ..
continue
try:
commit_ts = ref.commit.committed_date
except LookupError:
# GitPython does not properly handle PGP signed tags
log.exception("Error in commit: %s, ref: %s. Type: %s",
ref.commit, ref.path, type(ref))
continue
commit_age = int((NOW - commit_ts) / 86400) # days
log.debug(
"%s at %s is %3s days old",
ref.commit,
ref.path,
commit_age,
)
if commit_age > args.days_ago:
if args.dryrun:
log.info("Would delete old ref: %s (%s)", ref.path, ref.commit)
else:
log.info("Deleting old ref: %s (%s)", ref.path, ref.commit)
ref.delete(repo, ref.path)

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