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.
$ cat >> $HGRCPATH << EOF
> [extensions]
> share =
> EOF
store and revlogv1 are required in source
$ hg --config format.usestore=false init no-store
$ hg -R no-store debugupgraderepo
abort: cannot upgrade repository; requirement missing: store
[255]
$ hg init no-revlogv1
$ cat > no-revlogv1/.hg/requires << EOF
> dotencode
> fncache
> generaldelta
> store
> EOF
$ hg -R no-revlogv1 debugupgraderepo
abort: cannot upgrade repository; requirement missing: revlogv1
[255]
Cannot upgrade shared repositories
$ hg init share-parent
$ hg -q share share-parent share-child
$ hg -R share-child debugupgraderepo
abort: cannot upgrade repository; unsupported source requirement: shared
[255]
Do not yet support upgrading manifestv2 and treemanifest repos
$ hg --config experimental.manifestv2=true init manifestv2
$ hg -R manifestv2 debugupgraderepo
abort: cannot upgrade repository; unsupported source requirement: manifestv2
[255]
$ hg --config experimental.treemanifest=true init treemanifest
$ hg -R treemanifest debugupgraderepo
abort: cannot upgrade repository; unsupported source requirement: treemanifest
[255]
Cannot add manifestv2 or treemanifest requirement during upgrade
$ hg init disallowaddedreq
$ hg -R disallowaddedreq --config experimental.manifestv2=true --config experimental.treemanifest=true debugupgraderepo
abort: cannot upgrade repository; do not support adding requirement: manifestv2, treemanifest
[255]
An upgrade of a repository created with recommended settings only suggests optimizations
$ hg init empty
$ cd empty
$ hg debugupgraderepo
(no feature deficiencies found in existing repository)
performing an upgrade with "--run" will make the following changes:
requirements
preserved: dotencode, fncache, generaldelta, revlogv1, store
additional optimizations are available by specifying "--optimize <name>":
redeltaparent
deltas within internal storage will be recalculated to choose an optimal base revision where this was not already done; the size of the repository may shrink and various operations may become faster; the first time this optimization is performed could slow down upgrade execution considerably; subsequent invocations should not run noticeably slower
redeltamultibase
deltas within internal storage will be recalculated against multiple base revision and the smallest difference will be used; the size of the repository may shrink significantly when there are many merges; this optimization will slow down execution in proportion to the number of merges in the repository and the amount of files in the repository; this slow down should not be significant unless there are tens of thousands of files and thousands of merges
redeltaall
deltas within internal storage will always be recalculated without reusing prior deltas; this will likely make execution run several times slower; this optimization is typically not needed
--optimize can be used to add optimizations
$ hg debugupgrade --optimize redeltaparent
(no feature deficiencies found in existing repository)
performing an upgrade with "--run" will make the following changes:
requirements
preserved: dotencode, fncache, generaldelta, revlogv1, store
redeltaparent
deltas within internal storage will choose a new base revision if needed
additional optimizations are available by specifying "--optimize <name>":
redeltamultibase
deltas within internal storage will be recalculated against multiple base revision and the smallest difference will be used; the size of the repository may shrink significantly when there are many merges; this optimization will slow down execution in proportion to the number of merges in the repository and the amount of files in the repository; this slow down should not be significant unless there are tens of thousands of files and thousands of merges
redeltaall
deltas within internal storage will always be recalculated without reusing prior deltas; this will likely make execution run several times slower; this optimization is typically not needed
Various sub-optimal detections work
$ cat > .hg/requires << EOF
> revlogv1
> store
> EOF
$ hg debugupgraderepo
repository lacks features recommended by current config options:
fncache
long and reserved filenames may not work correctly; repository performance is sub-optimal
dotencode
storage of filenames beginning with a period or space may not work correctly
generaldelta
deltas within internal storage are unable to choose optimal revisions; repository is larger and slower than it could be; interaction with other repositories may require extra network and CPU resources, making "hg push" and "hg pull" slower
performing an upgrade with "--run" will make the following changes:
requirements
preserved: revlogv1, store
added: dotencode, fncache, generaldelta
fncache
repository will be more resilient to storing certain paths and performance of certain operations should be improved
dotencode
repository will be better able to store files beginning with a space or period
generaldelta
repository storage will be able to create optimal deltas; new repository data will be smaller and read times should decrease; interacting with other repositories using this storage model should require less network and CPU resources, making "hg push" and "hg pull" faster
additional optimizations are available by specifying "--optimize <name>":
redeltaparent
deltas within internal storage will be recalculated to choose an optimal base revision where this was not already done; the size of the repository may shrink and various operations may become faster; the first time this optimization is performed could slow down upgrade execution considerably; subsequent invocations should not run noticeably slower
redeltamultibase
deltas within internal storage will be recalculated against multiple base revision and the smallest difference will be used; the size of the repository may shrink significantly when there are many merges; this optimization will slow down execution in proportion to the number of merges in the repository and the amount of files in the repository; this slow down should not be significant unless there are tens of thousands of files and thousands of merges
redeltaall
deltas within internal storage will always be recalculated without reusing prior deltas; this will likely make execution run several times slower; this optimization is typically not needed
$ hg --config format.dotencode=false debugupgraderepo
repository lacks features recommended by current config options:
fncache
long and reserved filenames may not work correctly; repository performance is sub-optimal
generaldelta
deltas within internal storage are unable to choose optimal revisions; repository is larger and slower than it could be; interaction with other repositories may require extra network and CPU resources, making "hg push" and "hg pull" slower
repository lacks features used by the default config options:
dotencode
storage of filenames beginning with a period or space may not work correctly
performing an upgrade with "--run" will make the following changes:
requirements
preserved: revlogv1, store
added: fncache, generaldelta
fncache
repository will be more resilient to storing certain paths and performance of certain operations should be improved
generaldelta
repository storage will be able to create optimal deltas; new repository data will be smaller and read times should decrease; interacting with other repositories using this storage model should require less network and CPU resources, making "hg push" and "hg pull" faster
additional optimizations are available by specifying "--optimize <name>":
redeltaparent
deltas within internal storage will be recalculated to choose an optimal base revision where this was not already done; the size of the repository may shrink and various operations may become faster; the first time this optimization is performed could slow down upgrade execution considerably; subsequent invocations should not run noticeably slower
redeltamultibase
deltas within internal storage will be recalculated against multiple base revision and the smallest difference will be used; the size of the repository may shrink significantly when there are many merges; this optimization will slow down execution in proportion to the number of merges in the repository and the amount of files in the repository; this slow down should not be significant unless there are tens of thousands of files and thousands of merges
redeltaall
deltas within internal storage will always be recalculated without reusing prior deltas; this will likely make execution run several times slower; this optimization is typically not needed
$ cd ..
Upgrading a repository that is already modern essentially no-ops
$ hg init modern
$ hg -R modern debugupgraderepo --run
upgrade will perform the following actions:
requirements
preserved: dotencode, fncache, generaldelta, revlogv1, store
beginning upgrade...
repository locked and read-only
creating temporary repository to stage migrated data: $TESTTMP/modern/.hg/upgrade.* (glob)
(it is safe to interrupt this process any time before data migration completes)
data fully migrated to temporary repository
marking source repository as being upgraded; clients will be unable to read from repository
starting in-place swap of repository data
replaced files will be backed up at $TESTTMP/modern/.hg/upgradebackup.* (glob)
replacing store...
store replacement complete; repository was inconsistent for *s (glob)
finalizing requirements file and making repository readable again
removing temporary repository $TESTTMP/modern/.hg/upgrade.* (glob)
copy of old repository backed up at $TESTTMP/modern/.hg/upgradebackup.* (glob)
the old repository will not be deleted; remove it to free up disk space once the upgraded repository is verified
Upgrading a repository to generaldelta works
$ hg --config format.usegeneraldelta=false init upgradegd
$ cd upgradegd
$ touch f0
$ hg -q commit -A -m initial
$ touch f1
$ hg -q commit -A -m 'add f1'
$ hg -q up -r 0
$ touch f2
$ hg -q commit -A -m 'add f2'
$ hg debugupgraderepo --run
upgrade will perform the following actions:
requirements
preserved: dotencode, fncache, revlogv1, store
added: generaldelta
generaldelta
repository storage will be able to create optimal deltas; new repository data will be smaller and read times should decrease; interacting with other repositories using this storage model should require less network and CPU resources, making "hg push" and "hg pull" faster
beginning upgrade...
repository locked and read-only
creating temporary repository to stage migrated data: $TESTTMP/upgradegd/.hg/upgrade.* (glob)
(it is safe to interrupt this process any time before data migration completes)
migrating 9 total revisions (3 in filelogs, 3 in manifests, 3 in changelog)
migrating 341 bytes in store; 401 bytes tracked data
migrating 3 filelogs containing 3 revisions (0 bytes in store; 0 bytes tracked data)
finished migrating 3 filelog revisions across 3 filelogs; change in size: 0 bytes
migrating 1 manifests containing 3 revisions (157 bytes in store; 220 bytes tracked data)
finished migrating 3 manifest revisions across 1 manifests; change in size: 0 bytes
migrating changelog containing 3 revisions (184 bytes in store; 181 bytes tracked data)
finished migrating 3 changelog revisions; change in size: 0 bytes
finished migrating 9 total revisions; total change in store size: 0 bytes
data fully migrated to temporary repository
marking source repository as being upgraded; clients will be unable to read from repository
starting in-place swap of repository data
replaced files will be backed up at $TESTTMP/upgradegd/.hg/upgradebackup.* (glob)
replacing store...
store replacement complete; repository was inconsistent for *s (glob)
finalizing requirements file and making repository readable again
removing temporary repository $TESTTMP/upgradegd/.hg/upgrade.* (glob)
copy of old repository backed up at $TESTTMP/upgradegd/.hg/upgradebackup.* (glob)
the old repository will not be deleted; remove it to free up disk space once the upgraded repository is verified
Original requirements backed up
$ cat .hg/upgradebackup.*/requires
dotencode
fncache
revlogv1
store
generaldelta added to original requirements files
$ cat .hg/requires
dotencode
fncache
generaldelta
revlogv1
store
store directory has files we expect
$ ls .hg/store
00changelog.i
00manifest.i
data
fncache
undo
undo.backupfiles
undo.phaseroots
manifest should be generaldelta
$ hg debugrevlog -m | grep flags
flags : inline, generaldelta
verify should be happy
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
3 files, 3 changesets, 3 total revisions
old store should be backed up
$ ls .hg/upgradebackup.*/store
00changelog.i
00manifest.i
data
fncache
lock
phaseroots
undo
undo.backup.fncache
undo.backupfiles
undo.phaseroots
$ cd ..