view hgdemandimport/tracing.py @ 39862:5a9ab91e0a45

revlog: new API to emit revision data I recently refactored changegroup generation code to make it more storage agnostic. I made significant progress. But there is still a bit of work to be done. Specifically: * Changegroup code is looking at low-level storage attributes to influence sorting. Sorting should be done at the storage layer. * The linknode lookup and sorting code for ellipsis is very complicated. * Linknodes are just generally wonky because e.g. file storage doesn't know how to translate a linkrev to a changelog node. * We regressed performance when introducing the request-response objects. Having thought about this problem a bit, I think I've come up with a better interface for emitting revision deltas. This commit defines and implements that interface. See the docstring in repository.py for more info. This API adds 3 notable features over the previous one. First, it defers node ordering to the storage implementation in the common case but allows overriding as necessary. We have a facility for requesting an exact ordering (used in ellipsis mode). We have another facility for storage order (used for changelog). Second, we have an argument specifying assumptions about parents revisions. This can be used to force a fulltext revision when we don't know the receiver has a parent revision to delta against. Third, we can control whether revision data is emitted. This makes the API suitable as a generic "index data retrieval" API as well as for producing revision deltas - possibly in the same operation! The new API is much simpler: we no longer need a complicated "request" object to encapsulate the delta generation request. I'm optimistic this will restore performance loss associated with emitrevisiondeltas(). Storage unit tests for the new API have been implemented. Future commits will port existing consumers of emitrevisiondeltas() to the new API then remove emitrevisiondeltas(). Differential Revision: https://phab.mercurial-scm.org/D4722
author Gregory Szorc <gregory.szorc@gmail.com>
date Fri, 21 Sep 2018 14:28:21 -0700
parents 452790284a15
children d0b8a3cfd732
line wrap: on
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# Support code for event tracing in Mercurial. Lives in demandimport
# so it can also be used in demandimport.
#
# Copyright 2018 Google LLC.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
from __future__ import absolute_import

import contextlib
import os

_pipe = None
_checked = False

@contextlib.contextmanager
def log(whencefmt, *whenceargs):
    global _pipe, _session, _checked
    if _pipe is None:
        if _checked:
            yield
            return
        _checked = True
        if 'HGCATAPULTSERVERPIPE' not in os.environ:
            yield
            return
        _pipe = open(os.environ['HGCATAPULTSERVERPIPE'], 'w', 1)
        _session = os.environ.get('HGCATAPULTSESSION', 'none')
    whence = whencefmt % whenceargs
    try:
        # Both writes to the pipe are wrapped in try/except to ignore
        # errors, as we can see mysterious errors in here if the pager
        # is active. Presumably other conditions could trigger
        # problems too.
        try:
            _pipe.write('START %s %s\n' % (_session, whence))
        except IOError:
            pass
        yield
    finally:
        try:
            _pipe.write('END %s %s\n' % (_session, whence))
        except IOError:
            pass