jon-wei commented on a change in pull request #7133: 6088 - Time Ordering On
Scans
URL: https://github.com/apache/incubator-druid/pull/7133#discussion_r267144903
##########
File path:
processing/src/main/java/org/apache/druid/query/scan/ScanQueryRunnerFactory.java
##########
@@ -68,34 +81,117 @@ public ScanQueryRunnerFactory(
)
{
// in single thread and in jetty thread instead of processing thread
- return new QueryRunner<ScanResultValue>()
- {
- @Override
- public Sequence<ScanResultValue> run(
- final QueryPlus<ScanResultValue> queryPlus, final Map<String,
Object> responseContext
- )
- {
- // Note: this variable is effective only when queryContext has a
timeout.
- // See the comment of CTX_TIMEOUT_AT.
- final long timeoutAt = System.currentTimeMillis() +
QueryContexts.getTimeout(queryPlus.getQuery());
- responseContext.put(CTX_TIMEOUT_AT, timeoutAt);
+ return (queryPlus, responseContext) -> {
+ ScanQuery query = (ScanQuery) queryPlus.getQuery();
+ int numSegments = 0;
+ final Iterator<QueryRunner<ScanResultValue>> segmentIt =
queryRunners.iterator();
+ for (; segmentIt.hasNext(); numSegments++) {
+ segmentIt.next();
+ }
+ // Note: this variable is effective only when queryContext has a timeout.
+ // See the comment of CTX_TIMEOUT_AT.
+ final long timeoutAt = System.currentTimeMillis() +
QueryContexts.getTimeout(queryPlus.getQuery());
+ responseContext.put(CTX_TIMEOUT_AT, timeoutAt);
+ if (query.getOrder().equals(ScanQuery.Order.NONE)) {
+ // Use normal strategy
return Sequences.concat(
Sequences.map(
Sequences.simple(queryRunners),
- new Function<QueryRunner<ScanResultValue>,
Sequence<ScanResultValue>>()
- {
- @Override
- public Sequence<ScanResultValue> apply(final
QueryRunner<ScanResultValue> input)
- {
- return input.run(queryPlus, responseContext);
- }
- }
+ input -> input.run(queryPlus, responseContext)
)
);
+ } else if (query.getLimit() <=
scanQueryConfig.getMaxRowsQueuedForTimeOrdering()) {
+ // Use priority queue strategy
+ return sortAndLimitScanResultValues(
+ Sequences.concat(Sequences.map(
+ Sequences.simple(queryRunners),
+ input -> input.run(queryPlus, responseContext)
+ )),
+ query
+ );
+ } else if (numSegments <=
scanQueryConfig.getMaxSegmentsTimeOrderedInMemory()) {
Review comment:
I think this is considering too large of a set of segments, suppose I had
the following hourly granularity segments (with 2 shards per hour):
```
wikipedia_2016-06-27T01:00:00.000Z_2016-06-27T02:00:00.000Z_2019-03-19T21:38:31.492Z
wikipedia_2016-06-27T01:00:00.000Z_2016-06-27T02:00:00.000Z_2019-03-19T21:38:31.492Z_1
wikipedia_2016-06-27T02:00:00.000Z_2016-06-27T03:00:00.000Z_2019-03-19T21:38:31.492Z
wikipedia_2016-06-27T02:00:00.000Z_2016-06-27T03:00:00.000Z_2019-03-19T21:38:31.492Z_1
```
You could create two subsequences, one per hour:
```
wikipedia_2016-06-27T01:00:00.000Z_2016-06-27T02:00:00.000Z_2019-03-19T21:38:31.492Z
wikipedia_2016-06-27T01:00:00.000Z_2016-06-27T02:00:00.000Z_2019-03-19T21:38:31.492Z_1
```
and
```
wikipedia_2016-06-27T02:00:00.000Z_2016-06-27T03:00:00.000Z_2019-03-19T21:38:31.492Z
wikipedia_2016-06-27T02:00:00.000Z_2016-06-27T03:00:00.000Z_2019-03-19T21:38:31.492Z_1
```
where `maxSegmentsTimeOrderedInMemory` applies to each subsequence (you only
need to simultaneously read segment files that are partitions for the same time
period)
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