reduce allocations and speed up StringUtil.sanitizeString

[richardstartin]

This is a fix for some low hanging fruit found by a user with a heavy RealtimeToOfflineTask (see #8014) - a good amount of time is spent sanitising strings.

This change makes this method more efficient (less than half the allocation when truncation is required, and no allocation when it isn't, ~2x faster) by making better use of the String API:

@State(Scope.Benchmark)
public class BenchmarkSanitizeStringValue {

  @Param({"10", "100", "1000"})
  int _length;

  @Param("512")
  int _maxLength;

  String _string;

  @Setup(Level.Trial)
  public void setup() {
    byte[] bytes = new byte[_length];
    for (int i = 0; i < _length; i++) {
      bytes[i] = (byte) ('a' + ThreadLocalRandom.current().nextInt(26));
    }
    _string = new String(bytes, StandardCharsets.UTF_8);
  }

  @Benchmark
  public String sanitize() {
    return StringUtil.sanitizeStringValue(_string, _maxLength);
  }

  @Benchmark
  public String sanitizeNew() {
    return StringUtil.sanitizeStringValueNew(_string, _maxLength);
  }
}

Benchmark                                                              (_length)  (_maxLength)  Mode  Cnt     Score     Error   Units
BenchmarkSanitizeStringValue.sanitize                                         10           512  avgt    5    10.444 ±   0.213   ns/op
BenchmarkSanitizeStringValue.sanitize:·gc.alloc.rate.norm                     10           512  avgt    5    40.000 ±   0.001    B/op
BenchmarkSanitizeStringValue.sanitize                                        100           512  avgt    5    29.909 ±   1.637   ns/op
BenchmarkSanitizeStringValue.sanitize:·gc.alloc.rate.norm                    100           512  avgt    5   216.000 ±   0.001    B/op
BenchmarkSanitizeStringValue.sanitize                                       1000           512  avgt    5   203.566 ±  13.111   ns/op
BenchmarkSanitizeStringValue.sanitize:·gc.alloc.rate.norm                   1000           512  avgt    5  2568.000 ±   0.001    B/op
BenchmarkSanitizeStringValue.sanitizeNew                                      10           512  avgt    5     6.107 ±   0.369   ns/op
BenchmarkSanitizeStringValue.sanitizeNew:·gc.alloc.rate.norm                  10           512  avgt    5    ≈ 10⁻⁶              B/op
BenchmarkSanitizeStringValue.sanitizeNew                                     100           512  avgt    5    14.349 ±   0.261   ns/op
BenchmarkSanitizeStringValue.sanitizeNew:·gc.alloc.rate.norm                 100           512  avgt    5    ≈ 10⁻⁵              B/op
BenchmarkSanitizeStringValue.sanitizeNew                                    1000           512  avgt    5   102.201 ±   0.703   ns/op
BenchmarkSanitizeStringValue.sanitizeNew:·gc.alloc.rate.norm                1000           512  avgt    5   552.000 ±   0.001    B/op

[codecov-commenter]

Codecov Report

Merging #8013 (824d7aa) into master (bf4bb9a) will increase coverage by 0.98%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #8013      +/-   ##
============================================
+ Coverage     70.34%   71.32%   +0.98%     
  Complexity     4214     4214              
============================================
  Files          1596     1596              
  Lines         82778    82773       -5     
  Branches      12348    12347       -1     
============================================
+ Hits          58227    59036     +809     
+ Misses        20564    19742     -822     
- Partials       3987     3995       +8     

Flag	Coverage Δ
integration1	29.05% <25.00%> (+0.05%)	⬆️
integration2	27.59% <75.00%> (?)
unittests1	68.10% <100.00%> (-0.01%)	⬇️
unittests2	14.31% <0.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...java/org/apache/pinot/common/utils/StringUtil.java	100.00% <100.00%> (ø)
...he/pinot/segment/local/segment/store/IndexKey.java	70.00% <0.00%> (-10.00%)	⬇️
...ntroller/helix/core/minion/TaskMetricsEmitter.java	86.36% <0.00%> (-4.55%)	⬇️
.../org/apache/pinot/core/startree/StarTreeUtils.java	69.89% <0.00%> (-2.16%)	⬇️
.../aggregation/function/ModeAggregationFunction.java	88.37% <0.00%> (-0.28%)	⬇️
...va/org/apache/pinot/controller/ControllerConf.java	57.31% <0.00%> (ø)
...lix/core/realtime/PinotRealtimeSegmentManager.java	81.67% <0.00%> (ø)
...nction/DistinctCountBitmapAggregationFunction.java	47.15% <0.00%> (ø)
...ntroller/helix/core/PinotHelixResourceManager.java	64.73% <0.00%> (+0.07%)	⬆️
...server/starter/helix/HelixInstanceDataManager.java	81.50% <0.00%> (+0.57%)	⬆️
... and 87 more

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