This unified construction removes most backend-specific code from
global.go. The backend registry will also enable integration tests to
use custom backends if necessary.
The ETA restic displays was based on a rate computed across the entire
backup operation. Often restic can progress at uneven rates. In the worst
case, restic progresses over most of the backup at a very high rate and
then finds new data to back up. The displayed ETA is then unrealistic and
never adapts.
Restic now estimates the transfer rate based on a sliding window, with the
goal of adapting to observed changes in rate. To avoid wild changes in the
estimate, several heuristics are used to keep the sliding window wide
enough to be relatively stable.
In order to change the backend initialization in `global.go` to be able
to generically call cfg.ApplyEnvironment() for supported backends, the
`interface{}` returned by `ParseConfig` must contain a pointer to the
configuration.
An alternative would be to use reflection to convert the type from
`interface{}(Config)` to `interface{}(*Config)` (from value to pointer
type). However, this would just complicate the type mess further.
Iterating through the indexmap according to the bucket order has the
problem that all indexEntries are accessed in random order which is
rather cache inefficient.
As we already keep a list of all allocated blocks, just iterate through
it. This allows iterating through a batch of indexEntries without random
memory accesses. In addition, the packID will likely remain similar
across multiple blobs as all blobs of a pack file are added as a single
batch.
This data structure reduces the wasted memory to O(sqrt(n)). The
top-layer of the hashed array tree (HAT) also has a size of O(sqrt(n)),
which makes it cache efficient. The top-layer should be small enough to
easily fit into the CPU cache and thus only adds little overhead
compared to directly accessing an index entry via a pointer.
The indexEntry objects are now allocated in a separate array. References
to an indexEntry are now stored as array indices. This has the benefit
of allowing the garbage collector to ignore the indexEntry objects as
these do not contain pointers and are part of a single large allocation.
New and its helpers used to create the cache directories several times
over. They now only do so once. The added test ensures that the cache is
produced in a consistent state when parts are deleted.
Use the logging methods from testing.TB to make use of tb.Helper(). This
allows the tests to log the filename and line number in which the test
helper was called. Previously the test helper was logged which is rarely
useful.
This function casts its argument to int32 before passing it to the
system call, so that big-endian CPUs read the lower rather than the
upper 32 bits of the pid.
This also gets rid of the last import of "unsafe" in the Unix build.
I changed syscall to x/sys/unix while I was at it, to remove one more
import line. The constants and types there are aliases for their syscall
counterparts.
