The TreeNodeIterator decodes nodes while iterating over a tree blob.
This should reduce peak memory usage as now only the serialized tree
blob and a single node have to alive at the same time. Using the
iterator has implications for the error handling however. Now it is
necessary that all loops that iterate through a tree check for errors
before using the node returned by the iterator.
The other change is that it is no longer possible to iterate over a tree
multiple times. Instead it must be loaded a second time. This only
affects the tree rewriting code.
The tree.Nodes will be replaced by an iterator to loads and serializes
tree node ondemand. Thus, the processing moves from StreamTrees into the
callback. Schedule them onto the workers used by StreamTrees for proper
load distribution.
This ensures that the pack header is actually read completely.
Previously, for a truncated file it was possible to only read a part of
the header, as backend.Load(...) is not guaranteed to return as many
bytes as requested by the length parameter.
Due to the interface of streamPack, we cannot guarantee that operations
progress fast enough that the underlying connections remains open. This
introduces partial failures which massively complicate the error
handling.
Switch to a simpler approach that retrieves the pack in chunks of 32MB.
If a blob is larger than this limit, then it is downloaded separately.
To avoid multiple copies in memory, an auxiliary interface
`discardReader` is introduced that allows directly accessing the
downloaded byte slices, while still supporting the streaming used by the
`check` command.
To only stream the content of a pack file once, check used StreamPack
with a custom pack load function. This combination was always brittle
and complicates using StreamPack everywhere else. Now that StreamPack
internally uses PackBlobIterator use that primitive instead, which is a
much better fit for what the check command requires.
For now, the guide is only shown if the blob content does not match its
hash. The main intended usage is to handle data corruption errors when
using maximum compression in restic 0.16.0
The ioutil functions are deprecated since Go 1.17 and only wrap another
library function. Thus directly call the underlying function.
This commit only mechanically replaces the function calls.
Repositories with mixed packs are probably quite rare by now. When
loading data blobs from a mixed pack file, this will no longer trigger
caching that file. However, usually tree blobs are accessed first such
that this shouldn't make much of a difference.
The checker gets a simpler replacement.
Sending data through a channel at very high frequency is extremely
inefficient. Thus use simple callbacks instead of channels.
> name old time/op new time/op delta
> MasterIndexEach-16 6.68s ±24% 0.96s ± 2% -85.64% (p=0.008 n=5+5)
Use runtime.GOMAXPROCS(0) as worker count for CPU-bound tasks,
repo.Connections() for IO-bound task and a combination if a task can be
both. Streaming packs is treated as IO-bound as adding more worker
cannot provide a speedup.
Typical IO-bound tasks are download / uploading / deleting files.
Decoding / Encoding / Verifying are usually CPU-bound. Several tasks are
a combination of both, e.g. for combined download and decode functions.
In the latter case add both limits together. As the backends have their
own concurrency limits restic still won't download more than
repo.Connections() files in parallel, but the additional workers can
decode already downloaded data in parallel.
Michael Eischer
Winfried Plappert
Alexander Neumann
Andrea Gelmini
greatroar