HDDS-2445. Replace ToStringBuilder in BlockData

[adoroszlai]

What changes were proposed in this pull request?

Eliminate ToStringBuilder from BlockData. Use a single StringBuilder to collect parts of the final result.

Also avoid stream-processing in setChunks for the special cases of 0 or 1 elements.

https://issues.apache.org/jira/browse/HDDS-2445

How was this patch tested?

Added benchmark with various implementations.

bin/ozone genesis -benchmark BenchmarkBlockDataToString

Normalized GC allocation rates are below (absolute values are not important, only relative to one another). Using a single string builder saves ~78% of allocations compared to the current implementation (ToStringBuilderDefaultCapacity).

Benchmark                  (capacity)  (count)   Mode  Cnt        Score       Error   Units
PushDownStringBuilder             112     1000  thrpt   20   503403.364 ±     6.593    B/op
InlineStringBuilder               112     1000  thrpt   20   503625.761 ±     2.665    B/op
SimpleStringBuilder               112     1000  thrpt   20  1133643.831 ±     4.051    B/op
ToStringBuilder                   112     1000  thrpt   20  1429626.864 ±     7.415    B/op
Concatenation                     112     1000  thrpt   20  1523808.749 ±    13.819    B/op
ToStringBuilderDefaultCapacity    N/A     1000  thrpt   20  2229699.096 ±     6.739    B/op

(Tested various capacities with the same benchmark to come up with final value of 112.)

Added a simple unit test to verify the output is unchanged.

Stream-processing change is verified by existing TestBlockData#testSetChunks.

[adoroszlai]

/retest

[elek]

+1

thanks the patch @adoroszlai

[adoroszlai]

Thanks @elek for reviewing and merging it.