GroupBy query cannot use result cache on broker

[hqx871]

Hi, I want to enable result cache on broker, but I found it does not support group by query. However, more than 50% of our query is group by query. Hope help.

[FrankChen021]

cache does not work for groupBy v2 queries. See #11370

[abhishekagarwal87]

I think we can enable result-level caching on broker for groupBy v2. caching is disabled even before result-level caching came to the fore.

[hqx871]

I finally found the cause from #3820 [groupBy v2: Results not fully merged when caching is enabled on the broker]. May be we can just disable the segment-level cache on broker and enable result-level cache.

[hqx871]

Thanks @abhishekagarwal87 and @FrankChen021. I have successfully reproduced the problem described by the PR #3820 [groupBy v2: Results not fully merged when caching is enabled on the broker] by following step:

1. make GroupByStrategyV2#isCacheable to return true.
2. ingestion the wikiticker-2015-09-12-sampled.json.gz by dynamic partition it into 20 segments with each no more than 2000 rows.
3. set druid.broker.cache.useCache and druid.broker.cache.populateCache to be true for broker
4. then take a sql as follow, and I finally got some partialy merged row, i.e {time='2015-09-12T02:00:00.000Z', channel = '#es.wikipedia', namespace = 'Main'}

select TIME_FLOOR(__time,'PT1H') "time",
channel,
namespace,
sum(added) sum_added
from wikipedia
where __time >='2015-09-12T00:00:00.000Z'
and __time <'2015-09-13T00:00:00.000Z'
GROUP BY TIME_FLOOR(__time,'PT1H'),channel,namespace
limit 10000

Finally, as @abhishekagarwal87 said, I think we can enable result-level caching on broker for groupBy v2.