LakshSingla commented on code in PR #16707:
URL: https://github.com/apache/druid/pull/16707#discussion_r1695467166
##########
processing/src/main/java/org/apache/druid/frame/field/LongFieldReader.java:
##########
@@ -99,4 +107,135 @@ public boolean isNull()
return super._isNull();
}
}
+
+ @Override
+ public Column makeRACColumn(Frame frame, RowSignature signature, String
columnName)
+ {
+ return new LongFieldReaderColumn(frame, signature.indexOf(columnName),
signature.size());
+ }
+
+ private class LongFieldReaderColumn implements Column
+ {
+ private final Frame frame;
+ private final Memory dataRegion;
+ private final FieldPositionHelper coach;
+
+ public LongFieldReaderColumn(Frame frame, int columnIndex, int numFields)
+ {
+ this.frame = frame;
+ this.dataRegion = frame.region(RowBasedFrameWriter.ROW_DATA_REGION);
+
+ this.coach = new FieldPositionHelper(
+ frame,
+ frame.region(RowBasedFrameWriter.ROW_OFFSET_REGION),
+ dataRegion,
+ columnIndex,
+ numFields
+ );
+ }
+
+ @Nonnull
+ @Override
+ public ColumnAccessor toAccessor()
+ {
+ return new ColumnAccessor()
+ {
+ @Override
+ public ColumnType getType()
+ {
+ return ColumnType.LONG;
+ }
+
+ @Override
+ public int numRows()
+ {
+ return frame.numRows();
+ }
+
+ @Override
+ public boolean isNull(int rowNum)
+ {
+ final long fieldPosition = coach.computeFieldPosition(rowNum);
+ return dataRegion.getByte(fieldPosition) == getNullIndicatorByte();
+ }
+
+ @Nullable
+ @Override
+ public Object getObject(int rowNum)
+ {
+ final long fieldPosition = coach.computeFieldPosition(rowNum);
+
+ if (dataRegion.getByte(fieldPosition) == getNullIndicatorByte()) {
+ return null;
+ } else {
+ return getLongAtPosition(fieldPosition);
+ }
+ }
+
+ @Override
+ public double getDouble(int rowNum)
+ {
+ return getLong(rowNum);
+ }
+
+ @Override
+ public float getFloat(int rowNum)
+ {
+ return getLong(rowNum);
+ }
+
+ @Override
+ public long getLong(int rowNum)
+ {
+ final long fieldPosition = coach.computeFieldPosition(rowNum);
+
+ if (dataRegion.getByte(fieldPosition) == getNullIndicatorByte()) {
+ return 0L;
+ } else {
+ return getLongAtPosition(fieldPosition);
+ }
+ }
+
+ @Override
+ public int getInt(int rowNum)
+ {
+ return (int) getLong(rowNum);
+ }
+
+ @Override
+ public int compareRows(int lhsRowNum, int rhsRowNum)
+ {
+ long lhsPosition = coach.computeFieldPosition(lhsRowNum);
+ long rhsPosition = coach.computeFieldPosition(rhsRowNum);
+
+ final byte nullIndicatorByte = getNullIndicatorByte();
+ if (dataRegion.getByte(lhsPosition) == nullIndicatorByte) {
+ if (dataRegion.getByte(rhsPosition) == nullIndicatorByte) {
+ return 0;
+ } else {
+ return -1;
+ }
+ } else {
+ if (dataRegion.getByte(rhsPosition) == nullIndicatorByte) {
+ return 1;
+ } else {
+ return Long.compare(getLongAtPosition(lhsPosition),
getLongAtPosition(rhsPosition));
+ }
+ }
+ }
Review Comment:
If two fields of the same type are written in the frame - a represented as
[a0...aM] and b represented as [b0..bN] then if (a > b), then the bytewise
comparison of a's representation will be lexicographically greater than the
bytewise representation of b. Therefore, if a > b, a0 = b0, a1 == b1, ... ai ==
bi, a(i+1) > b(i+1)
Note, this only applies to primitive types and arrays of primitives.
We use this property in multiple places, check out one of the
implementations here -
https://github.com/apache/druid/blob/master/processing/src/main/java/org/apache/druid/frame/read/FrameReaderUtils.java#L173-L173.
in the given code, you can compare using something like:
```java
for (int i = 0; i < Math.min(fieldLength1, fieldLength2); ++i) {
int cmp = compareBytesUnsigned(dataRegion.getByte(fieldPosition1 + i),
dataRegion.getByte(fieldPosition2 + i);
if (cmp != 0) return cmp;
}
```
`fieldLength1` & `fieldLength2` is something you can compute by subtracting
the starting position of current field from the starting position of the next
field (or the row end). There are pre-existing utility methods that can
achieve this - checkout the classes `ReadableFieldPointer` and
`RowMemoryFieldPointer`. You can check those as well, I think some of the work
done by the `FieldPositionHelper` is duplicated in those classes, albeit in a
non-roundabout way.
LMK if there's more I can explain up on.
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