When downloading an url and the destination file exists but is empty,
avoid using http range to resume, since a range "bytes=0-" is an unusual
edge case that it's best to avoid relying on working.
This is known to fix a case where importfeed downloaded a partial feed from
such a server. Since importfeed uses withTmpFile, the destination always exists
empty, so it would particularly tickle such problem servers. Resuming from 0
is otherwise possible, but unlikely.
This means that Command.Move and Command.Get don't need to
manually set the stage, and is a lot cleaner conceptually.
Also, this makes Command.Sync.syncFile use the worker pool better.
In the scenario where it first downloads content and then uploads it to
some other remotes, it will start in TransferStage, then enter VerifyStage
and then go back to TransferStage for each transfer to the remotes.
Before, it entered CleanupStage after the download, and stayed in it for
the upload, so too many transfer jobs could run at the same time.
Note that, in Remote.Git, it uses runTransfer and also verifyKeyContent
inside onLocal. That has a Annex state for the remote, with no worker pool.
So the resulting calls to enteringStage won't block in there.
While Remote.Git.copyToRemote does do checksum verification, I
realized that should not use a verification slot in the WorkerPool
to do it. Because, it's reading back from eg, a removable disk to checksum.
That will contend with other writes to that disk. It's best to treat
that checksum verification as just part of the transer. So, removed the todo
item about that, as there's nothing needing to be done.
get, move, copy, sync: When -J or annex.jobs has enabled concurrency,
checksum verification uses a separate job pool than is used for
downloads, to keep bandwidth saturated.
Not yet done for upload checksum verification, but that only affects
remotes on local disks.
Avoid a delay at startup when concurrency is enabled and there are
rsync or gcrypt special remotes, which was caused by git-annex
opening a ssh connection to the remote too early.
sshOptions makes a connection to the ssh server if one is not already open,
when concurrency is enabled. Avoid doing that at startup, when the remote
list is being built, but the remote may not be used at all.
Instead, rsync/gcrypt now runs sshOptions once per ssh connection to the
server. This should not be significant overhead since Remote.Git already
has the same overhead (as do Bup and Ddar).
The hoped for optimisation of CommandStart with -J did not materialize.
In fact, not runnign CommandStart in parallel is slower than -J3.
So, CommandStart are still run in parallel.
(The actual bad performance I've been seeing with -J in my big repo
has to do with building the remoteList.)
But, this is still progress toward making -J faster, because it gets rid
of the onlyActionOn roadblock in the way of making CommandCleanup jobs
run separate from CommandPerform jobs.
Added OnlyActionOn constructor for ActionItem which fixes the
onlyActionOn breakage in the last commit.
Made CustomOutput include an ActionItem, so even things using it can
specify OnlyActionOn.
In Command.Move and Command.Sync, there were CommandStarts that used
includeCommandAction, so output messages, which is no longer allowed.
Fixed by using startingCustomOutput, but that's still not quite right,
since it prevents message display for the includeCommandAction run
inside it too.
When running multiple concurrent actions, the cleanup phase is run in a
separate queue than the main action queue. This can make some commands
faster, because less time is spent on bookkeeping in between each file
transfer.
But as far as I can see, nothing will be sped up much by this yet, because
all the existing cleanup actions are very light-weight. This is just groundwork
for deferring checksum verification to cleanup time.
This change does mean that if the user expects -J2 will mean that they see no
more than 2 jobs running at a time, they may be surprised to see 4 in some
cases (if the cleanup actions are slow enough to notice).
It might also make sense to enable background cleanup without the -J,
for at least one cleanup action. Indeed, that's the behavior that -J1
has now. At some point in the future, it make make sense to make the
behavior with no -J the same as -J1. The only reason it's not currently
is that git-annex can build w/o concurrent-output, and also any bugs
in concurrent-output (such as perhaps misbehaving on non-VT100 compatible
terminals) are avoided by default by only using it when -J is used.
