diff mercurial/repair.py @ 30779:38aa1ca97b6a

repair: migrate revlogs during upgrade

Our next step for in-place upgrade is to migrate store data. Revlogs
are the biggest source of data within the store and a store is useless
without them, so we implement their migration first.

Our strategy for migrating revlogs is to walk the store and call
`revlog.clone()` on each revlog. There are some minor complications.

Because revlogs have different storage options (e.g. changelog has
generaldelta and delta chains disabled), we need to obtain the
correct class of revlog so inserted data is encoded properly for its
type.

Various attempts at implementing progress indicators that didn't lead
to frustration from false "it's almost done" indicators were made.

I initially used a single progress bar based on number of revlogs.
However, this quickly churned through all filelogs, got to 99% then
effectively froze at 99.99% when it got to the manifest.

So I converted the progress bar to total revision count. This was a
little bit better. But the manifest was still significantly slower
than filelogs and it took forever to process the last few percent.

I then tried both revision/chunk bytes and raw bytes as the
denominator. This had the opposite effect: because so much data is in
manifests, it would churn through filelogs without showing much
progress. When it got to manifests, it would fill in 90+% of the
progress bar.

I finally gave up having a unified progress bar and instead implemented
3 progress bars: 1 for filelog revisions, 1 for manifest revisions, and
1 for changelog revisions. I added extra messages indicating the total
number of revisions of each so users know there are more progress bars
coming.

I also added extra messages before and after each stage to give extra
details about what is happening. Strictly speaking, this isn't
necessary. But the numbers are impressive. For example, when converting
a non-generaldelta mozilla-central repository, the messages you see are:

   migrating 2475593 total revisions (1833043 in filelogs, 321156 in manifests, 321394 in changelog)
   migrating 1.67 GB in store; 2508 GB tracked data
   migrating 267868 filelogs containing 1833043 revisions (1.09 GB in store; 57.3 GB tracked data)
   finished migrating 1833043 filelog revisions across 267868 filelogs; change in size: -415776 bytes
   migrating 1 manifests containing 321156 revisions (518 MB in store; 2451 GB tracked data)

That "2508 GB" figure really blew me away. I had no clue that the raw
tracked data in mozilla-central was that large. Granted, 2451 GB is in
the manifest and "only" 57.3 GB is in filelogs. But still.

It's worth noting that gratuitous loading of source revlogs in order
to display numbers and progress bars does serve a purpose: it ensures
we can open all source revlogs. We don't want to spend several minutes
copying revlogs only to encounter a permissions error or similar later.

As part of this commit, we also add swapping of the store directory
to the upgrade function. After revlogs are converted, we move the
old store into the backup directory then move the temporary repo's
store into the old store's location. On well-behaved systems, this
should be 2 atomic operations and the window of inconsistency show be
very narrow.

There are still a few improvements to be made to store copying and
upgrading. But this commit gets the bulk of the work out of the way.

--- a/mercurial/repair.py	Sun Dec 18 17:02:57 2016 -0800
+++ b/mercurial/repair.py	Sun Dec 18 17:00:15 2016 -0800
@@ -11,15 +11,19 @@
 import errno
 import hashlib
 import tempfile
+import time
 
 from .i18n import _
 from .node import short
 from . import (
     bundle2,
     changegroup,
+    changelog,
     error,
     exchange,
+    manifest,
     obsolete,
+    revlog,
     scmutil,
     util,
 )
@@ -639,6 +643,162 @@
 
     return newactions
 
+def _revlogfrompath(repo, path):
+    """Obtain a revlog from a repo path.
+
+    An instance of the appropriate class is returned.
+    """
+    if path == '00changelog.i':
+        return changelog.changelog(repo.svfs)
+    elif path.endswith('00manifest.i'):
+        mandir = path[:-len('00manifest.i')]
+        return manifest.manifestrevlog(repo.svfs, dir=mandir)
+    else:
+        # Filelogs don't do anything special with settings. So we can use a
+        # vanilla revlog.
+        return revlog.revlog(repo.svfs, path)
+
+def _copyrevlogs(ui, srcrepo, dstrepo, tr, deltareuse, aggressivemergedeltas):
+    """Copy revlogs between 2 repos."""
+    revcount = 0
+    srcsize = 0
+    srcrawsize = 0
+    dstsize = 0
+    fcount = 0
+    frevcount = 0
+    fsrcsize = 0
+    frawsize = 0
+    fdstsize = 0
+    mcount = 0
+    mrevcount = 0
+    msrcsize = 0
+    mrawsize = 0
+    mdstsize = 0
+    crevcount = 0
+    csrcsize = 0
+    crawsize = 0
+    cdstsize = 0
+
+    # Perform a pass to collect metadata. This validates we can open all
+    # source files and allows a unified progress bar to be displayed.
+    for unencoded, encoded, size in srcrepo.store.walk():
+        if unencoded.endswith('.d'):
+            continue
+
+        rl = _revlogfrompath(srcrepo, unencoded)
+        revcount += len(rl)
+
+        datasize = 0
+        rawsize = 0
+        idx = rl.index
+        for rev in rl:
+            e = idx[rev]
+            datasize += e[1]
+            rawsize += e[2]
+
+        srcsize += datasize
+        srcrawsize += rawsize
+
+        # This is for the separate progress bars.
+        if isinstance(rl, changelog.changelog):
+            crevcount += len(rl)
+            csrcsize += datasize
+            crawsize += rawsize
+        elif isinstance(rl, manifest.manifestrevlog):
+            mcount += 1
+            mrevcount += len(rl)
+            msrcsize += datasize
+            mrawsize += rawsize
+        elif isinstance(rl, revlog.revlog):
+            fcount += 1
+            frevcount += len(rl)
+            fsrcsize += datasize
+            frawsize += rawsize
+
+    if not revcount:
+        return
+
+    ui.write(_('migrating %d total revisions (%d in filelogs, %d in manifests, '
+               '%d in changelog)\n') %
+             (revcount, frevcount, mrevcount, crevcount))
+    ui.write(_('migrating %s in store; %s tracked data\n') % (
+             (util.bytecount(srcsize), util.bytecount(srcrawsize))))
+
+    # Used to keep track of progress.
+    progress = []
+    def oncopiedrevision(rl, rev, node):
+        progress[1] += 1
+        srcrepo.ui.progress(progress[0], progress[1], total=progress[2])
+
+    # Do the actual copying.
+    # FUTURE this operation can be farmed off to worker processes.
+    seen = set()
+    for unencoded, encoded, size in srcrepo.store.walk():
+        if unencoded.endswith('.d'):
+            continue
+
+        oldrl = _revlogfrompath(srcrepo, unencoded)
+        newrl = _revlogfrompath(dstrepo, unencoded)
+
+        if isinstance(oldrl, changelog.changelog) and 'c' not in seen:
+            ui.write(_('finished migrating %d manifest revisions across %d '
+                       'manifests; change in size: %s\n') %
+                     (mrevcount, mcount, util.bytecount(mdstsize - msrcsize)))
+
+            ui.write(_('migrating changelog containing %d revisions '
+                       '(%s in store; %s tracked data)\n') %
+                     (crevcount, util.bytecount(csrcsize),
+                      util.bytecount(crawsize)))
+            seen.add('c')
+            progress[:] = [_('changelog revisions'), 0, crevcount]
+        elif isinstance(oldrl, manifest.manifestrevlog) and 'm' not in seen:
+            ui.write(_('finished migrating %d filelog revisions across %d '
+                       'filelogs; change in size: %s\n') %
+                     (frevcount, fcount, util.bytecount(fdstsize - fsrcsize)))
+
+            ui.write(_('migrating %d manifests containing %d revisions '
+                       '(%s in store; %s tracked data)\n') %
+                     (mcount, mrevcount, util.bytecount(msrcsize),
+                      util.bytecount(mrawsize)))
+            seen.add('m')
+            progress[:] = [_('manifest revisions'), 0, mrevcount]
+        elif 'f' not in seen:
+            ui.write(_('migrating %d filelogs containing %d revisions '
+                       '(%s in store; %s tracked data)\n') %
+                     (fcount, frevcount, util.bytecount(fsrcsize),
+                      util.bytecount(frawsize)))
+            seen.add('f')
+            progress[:] = [_('file revisions'), 0, frevcount]
+
+        ui.progress(progress[0], progress[1], total=progress[2])
+
+        ui.note(_('cloning %d revisions from %s\n') % (len(oldrl), unencoded))
+        oldrl.clone(tr, newrl, addrevisioncb=oncopiedrevision,
+                    deltareuse=deltareuse,
+                    aggressivemergedeltas=aggressivemergedeltas)
+
+        datasize = 0
+        idx = newrl.index
+        for rev in newrl:
+            datasize += idx[rev][1]
+
+        dstsize += datasize
+
+        if isinstance(newrl, changelog.changelog):
+            cdstsize += datasize
+        elif isinstance(newrl, manifest.manifestrevlog):
+            mdstsize += datasize
+        else:
+            fdstsize += datasize
+
+    ui.progress(progress[0], None)
+
+    ui.write(_('finished migrating %d changelog revisions; change in size: '
+               '%s\n') % (crevcount, util.bytecount(cdstsize - csrcsize)))
+
+    ui.write(_('finished migrating %d total revisions; total change in store '
+               'size: %s\n') % (revcount, util.bytecount(dstsize - srcsize)))
+
 def _upgraderepo(ui, srcrepo, dstrepo, requirements, actions):
     """Do the low-level work of upgrading a repository.
 
@@ -652,7 +812,25 @@
     assert srcrepo.currentwlock()
     assert dstrepo.currentwlock()
 
-    # TODO copy store
+    ui.write(_('(it is safe to interrupt this process any time before '
+               'data migration completes)\n'))
+
+    if 'redeltaall' in actions:
+        deltareuse = revlog.revlog.DELTAREUSENEVER
+    elif 'redeltaparent' in actions:
+        deltareuse = revlog.revlog.DELTAREUSESAMEREVS
+    elif 'redeltamultibase' in actions:
+        deltareuse = revlog.revlog.DELTAREUSESAMEREVS
+    else:
+        deltareuse = revlog.revlog.DELTAREUSEALWAYS
+
+    with dstrepo.transaction('upgrade') as tr:
+        _copyrevlogs(ui, srcrepo, dstrepo, tr, deltareuse,
+                     'redeltamultibase' in actions)
+
+    # TODO copy non-revlog store files
+
+    ui.write(_('data fully migrated to temporary repository\n'))
 
     backuppath = tempfile.mkdtemp(prefix='upgradebackup.', dir=srcrepo.path)
     backupvfs = scmutil.vfs(backuppath)
@@ -673,7 +851,16 @@
     ui.write(_('replaced files will be backed up at %s\n') %
              backuppath)
 
-    # TODO do the store swap here.
+    # Now swap in the new store directory. Doing it as a rename should make
+    # the operation nearly instantaneous and atomic (at least in well-behaved
+    # environments).
+    ui.write(_('replacing store...\n'))
+    tstart = time.time()
+    util.rename(srcrepo.spath, backupvfs.join('store'))
+    util.rename(dstrepo.spath, srcrepo.spath)
+    elapsed = time.time() - tstart
+    ui.write(_('store replacement complete; repository was inconsistent for '
+               '%0.1fs\n') % elapsed)
 
     # We first write the requirements file. Any new requirements will lock
     # out legacy clients.