jt2594838 commented on a change in pull request #2859:
URL: https://github.com/apache/iotdb/pull/2859#discussion_r595798710
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File path:
server/src/main/java/org/apache/iotdb/db/query/aggregation/impl/FirstValueAggrResult.java
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@@ -94,11 +94,26 @@ public void updateResultUsingTimestamps(
if (hasFinalResult()) {
return;
}
+ for (int i = 0; i < length; i++) {
+ long[] oneTimestamp = new long[1];
+ oneTimestamp[0] = timestamps[i];
+ Object[] values = dataReader.getValuesInTimestamps(oneTimestamp, 1);
+ if (values[0] != null) {
+ setValue(values[0]);
+ timestamp = timestamps[i];
+ break;
+ }
+ }
Review comment:
This has a potential performance problem when there are many null values
in the front. For example, `timestamps.length == 1000` but the first 999 values
are all null, then you will have to call `dataReader.getValuesInTimestamps` for
a thousand times, which may incur some overhead.
My suggestion would be to add an interface `getFirstValueInTimestamps` in
`dataReader` which returns the first non-null value that is in the given
timestamps.
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