This is to utilize an optimized version of
sha256 checksum which @fwessels implemented.
blake2b lacks such optimizations on ARM platform,
this can provide us significant boost in performance.
blake2b on ARM64 as expected would be slower.
```
BenchmarkSize1K-4 30000 44015 ns/op 23.26 MB/s
BenchmarkSize8K-4 5000 335448 ns/op 24.42 MB/s
BenchmarkSize32K-4 1000 1333960 ns/op 24.56 MB/s
BenchmarkSize128K-4 300 5328286 ns/op 24.60 MB/s
```
sha256 on ARM64 is faster by orders of magnitude giving close to
AVX performance of blake2b.
```
BenchmarkHash8Bytes-4 1000000 1446 ns/op 5.53 MB/s
BenchmarkHash1K-4 500000 3229 ns/op 317.12 MB/s
BenchmarkHash8K-4 100000 14430 ns/op 567.69 MB/s
BenchmarkHash1M-4 1000 1640126 ns/op 639.33 MB/s
```
This change brings in changes at multiple places
- Reuse buffers at almost all locations ranging
from rpc, fs, xl, checksum etc.
- Change caching behavior to disable itself
under low memory conditions i.e < 8GB of RAM.
- Only objects cached are of size 1/10th the size
of the cache for example if 4GB is the cache size
the maximum object size which will be cached
is going to be 400MB. This change is an
optimization to cache more objects rather
than few larger objects.
- If object cache is enabled default GC
percent has been reduced to 20% in lieu
with newly found behavior of GC. If the cache
utilization reaches 75% of the maximum value
GC percent is reduced to 10% to make GC
more aggressive.
- Do not use *bytes.Buffer* due to its growth
requirements. For every allocation *bytes.Buffer*
allocates an additional buffer for its internal
purposes. This is undesirable for us, so
implemented a new cappedWriter which is capped to a
desired size, beyond this all writes rejected.
Possible fix for #3403.
Harshavardhana
Andreas Auernhammer
Krishna Srinivas