[jira] [Created] (KAFKA-13973) block-cache-capacity metrics worth twice as much as normal

["Sylvain Le Gouellec (Jira)" <ji...@apache.org>]

Sylvain Le Gouellec created KAFKA-13973:
-------------------------------------------

             Summary: block-cache-capacity metrics worth twice as much as normal
                 Key: KAFKA-13973
                 URL: https://issues.apache.org/jira/browse/KAFKA-13973
             Project: Kafka
          Issue Type: Bug
          Components: streams
    Affects Versions: 3.2.0
            Reporter: Sylvain Le Gouellec
         Attachments: Screenshot 2022-06-09 at 08.55.36.png

I have created a very simple kafka-streams application with 1 state store. I'm very surprised that the block-cache-capacity metrics show a {{100MB}} block cache capacity instead of the default one in kafka streams is {{{}50MB{}}}.
 
My topology :
StreamsBuilder sb = new StreamsBuilder();
sb.stream("input")
        .groupByKey()
        .count()
        .toStream()
        .to("output");
 
I checkout the {{kafka-streams}} code and I saw a strange thing. When the {{{}RocksDBTimestampedStore{}}}store is created, we try to create two column families for backward compatibility with a potentiel old key/value store.

In this method, {{setDbAccessor(col1, col2)}} if the first column is not valid, well you close this one ([L102|https://github.com/apache/kafka/blob/4542acdc14d5ec3daa1f36d8dc24abc244ee24ff/streams/src/main/java/org/apache/kafka/streams/state/internals/RocksDBTimestampedStore.java#L102]). But regarding the rocksdb instance, it's seems that the column families is not deleted completely and the metrics exposed by [Rocksdb continue to aggregate (L373)|https://github.com/apache/kafka/blob/4542acdc14d5ec3daa1f36d8dc24abc244ee24ff/streams/src/main/java/org/apache/kafka/streams/state/internals/metrics/RocksDBMetricsRecorder.java#L373] {{block-cache-capacity }}for both column families (default and keyValueWithTimestamp).

Maybe you have to drop explicitly the column family, in the {{setDbAccessor(col1, col2)}} if the first column is not valid (like {{{}db.dropColumnFamily(noTimestampColumnFamily);{}}})
 
I tried to drop the {{noTimestampColumnFamily in setDbAccessor if the first column is not valid like : }}



 
{code:java}
private void setDbAccessor(final ColumnFamilyHandle noTimestampColumnFamily,
                           final ColumnFamilyHandle withTimestampColumnFamily) throws RocksDBException {
    final RocksIterator noTimestampsIter = db.newIterator(noTimestampColumnFamily);
    noTimestampsIter.seekToFirst();
    if (noTimestampsIter.isValid()) {
        log.info("Opening store {} in upgrade mode", name);
        dbAccessor = new DualColumnFamilyAccessor(noTimestampColumnFamily, withTimestampColumnFamily);
    } else {
        log.info("Opening store {} in regular mode", name);
        dbAccessor = new SingleColumnFamilyAccessor(withTimestampColumnFamily);
        noTimestampColumnFamily.close();
        db.dropColumnFamily(noTimestampColumnFamily); // try fix it
    }
    noTimestampsIter.close();
}{code}
 

 

 

{{But it's seems that you can't drop the default column family in RocksDb (see screenshot).}}

{{*So how can we have the real block-cache-capacity metrics value in Kafka Streams monitoring ?* }}



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