Gary Lam created FLINK-37109:
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Summary: Increase state processor API performance when reading
keyed rocksdb state
Key: FLINK-37109
URL: https://issues.apache.org/jira/browse/FLINK-37109
Project: Flink
Issue Type: Improvement
Components: API / State Processor
Reporter: Gary Lam
Could we allow for duplicates via a flag when reading keyed rocksdb state, to
improve performance?
>From the [mailing list
>discussion,|https://www.mail-archive.com/user@flink.apache.org/msg43863.html]
>when the state processor api reads from state, it does multiple reads/writes
>to avoid duplicates:
{code:java}
The trick we perform is to delete keys from rocksDB after each read, so we can
do full table scans on all column families but never see any duplicates.{code}
In my application, which has a keyed state of size ~200GB, I have found it
takes >4 hours to iterate the entire state. Doing a CPU profile, 70% of the
time is spent on the `remove()` rocksdb call.
If I comment out [this
line|https://github.com/apache/flink/blob/26436ac27ae9e4705910b0502abb5bdd33ec686b/flink-libraries/flink-state-processing-api/src/main/java/org/apache/flink/state/api/input/KeyedStateInputFormat.java#L229]
`keysAndNamespaces.remove();`, I can read the entire state in <15 minutes, and
my particular application (trying to detect outliers in the state) is robust to
duplicates.
Thus if we allow this to be a user configurable flag (to skip deduplication) it
would give a performance boost to users who don't care about deduplication.
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