Fokko commented on code in PR #3465:
URL: https://github.com/apache/parquet-java/pull/3465#discussion_r3156563556
##########
parquet-column/src/main/java/org/apache/parquet/column/values/deltastrings/DeltaByteArrayWriter.java:
##########
@@ -88,14 +89,19 @@ public String memUsageString(String prefix) {
@Override
public void writeBytes(Binary v) {
- int i = 0;
- byte[] vb = v.getBytes();
- int length = previous.length < vb.length ? previous.length : vb.length;
- // find the number of matching prefix bytes between this value and the
previous one
- for (i = 0; (i < length) && (previous[i] == vb[i]); i++)
- ;
+ byte[] vb = v.getBytesUnsafe();
Review Comment:
```suggestion
byte[] vb = v.isBackingBytesReused() ? v.getBytes() : v.getBytesUnsafe();
```
##########
parquet-column/src/main/java/org/apache/parquet/column/values/deltastrings/DeltaByteArrayWriter.java:
##########
@@ -88,14 +89,19 @@ public String memUsageString(String prefix) {
@Override
public void writeBytes(Binary v) {
- int i = 0;
- byte[] vb = v.getBytes();
- int length = previous.length < vb.length ? previous.length : vb.length;
- // find the number of matching prefix bytes between this value and the
previous one
- for (i = 0; (i < length) && (previous[i] == vb[i]); i++)
- ;
+ byte[] vb = v.getBytesUnsafe();
+ int length = Math.min(previous.length, vb.length);
+ // Find the number of matching prefix bytes between this value and the
previous one.
+ // Arrays.mismatch is intrinsified by the JVM to use SIMD instructions.
+ int i = Arrays.mismatch(previous, 0, length, vb, 0, length);
+ if (i < 0) {
+ i = length; // all bytes in the common range matched
+ }
prefixLengthWriter.writeInteger(i);
suffixWriter.writeBytes(v.slice(i, vb.length - i));
- previous = vb;
+ // Retain an owned copy for prefix comparison with the next value.
+ // getBytesUnsafe() may return the backing array directly, so we must copy
+ // if the Binary's backing bytes may be reused by the caller.
+ previous = v.isBackingBytesReused() ? v.getBytes() : vb;
Review Comment:
```suggestion
previous = vb;
```
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