Matthias J. Sax created KAFKA-7420:
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Summary: Global stores should be guarded as read-only for regular
tasks
Key: KAFKA-7420
URL: https://issues.apache.org/jira/browse/KAFKA-7420
Project: Kafka
Issue Type: Improvement
Components: streams
Reporter: Matthias J. Sax
Global stores should only be update by the global thread. Any other task,
should only read from a global store. However, when getting a reference to a
global store, all tasks have full read/write access to the store.
We should put a guard in place and only return either _(a)_ a read-only store,
or _(b)_ wrap the store but throw an exception on write for regular tasks.
While the read-only store idea might be cleaner from an API point of view, we
should consider the second approach for 2 reasons: (1) it's backwards
compatible (of course, code might fail at runtime, but this seems to be ok, as
it indicates a bug in the user code anyway) (2) with regard to
[KIP-358|https://cwiki.apache.org/confluence/display/KAFKA/KIP-358%3A+Migrate+Streams+API+to+Duration+instead+of+long+ms+times],
we should have the more runtime efficient methods at this level (currently,
global stores are only key-value stores and this argument falls a little short
though—however, it might be a good idea to stay future proof; at least, we
should discuss it).
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