Previously bytesutil.Resize() was copying the original byte slice contents to a newly allocated slice.
This wasted CPU cycles and memory bandwidth in some places, where the original slice contents wasn't needed
after slize resizing. Switch such places to bytesutil.ResizeNoCopy().
Rename the original bytesutil.Resize() function to bytesutil.ResizeWithCopy() for the sake of improved readability.
Additionally, allocate new slice with `make()` instead of `append()`. This guarantees that the capacity of the allocated slice
exactly matches the requested size. The `append()` could return a slice with bigger capacity as an optimization for further `append()` calls.
This could result in excess memory usage when the returned byte slice was cached (for instance, in lib/blockcache).
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2007
The strategy is:
- Periodical flushing of inmemory blocks to files, so they aren't lost on unclean shutdown.
- Periodical syncing of metadata for persisted queues, so the metadata remains in sync with the persisted data.
- Automatic adjusting of too big chunk size when opening the queue. The chunk size may be bigger than the writer offset after unclean shutdown.
- Skipping of broken chunk file if it cannot be read.
- Fsyncing finalized chunk files.
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/687
Metric `vm_persistentqueue_bytes_pending` is a gauge that shows current amount
of bytes in persistentqueue flushed on disk as a difference between write and read
offsets. This metric is very similar to `vmagent_remotewrite_pending_data_bytes`
except of accounting for bytes in-memory.
