LakshSingla opened a new pull request, #15525:
URL: https://github.com/apache/druid/pull/15525
### Description
This PR fixes a bug with the long string pair serde where null and empty
strings are treated equivalently, and the return value is always null. When
'useDefaultValueForNull' was set to true by default, this wasn't a commonly
seen issue, because nulls were equivalent to empty strings. However, since the
default has changed to false, this can create incorrect results when the long
string pairs are serded, where the empty strings are incorrectly converted to
nulls.
Original behavior:
| value | deserialize(serialize(value)) | round trip is same |
|--------|--------|--------|
| new SerializablePairLongString(123, null) | new
SerializablePairLongString(123, null) | Yes, behaviour is correct |
| new SerializablePairLongString(123, "") | new
SerializablePairLongString(123, null) | No, behaviour is incorrect |
New behavior:
| value | deserialize(serialize(value)) | round trip is same |
|--------|--------|--------|
| new SerializablePairLongString(123, null) | new
SerializablePairLongString(123, null) | Yes, behaviour is correct |
| new SerializablePairLongString(123, "") | new
SerializablePairLongString(123, "") | Yes, behaviour is correct |
<hr>
Note, this now opens up possibilities of reading and writing with the
different versions of the serdes - the new serde can deserialize the serialized
value from the older serde, and the older serde can deserialize the value from
the newer serde (during cluster upgrade and rollback)
The behavior in those cases will be:
(note: P(123, null) is equivalent to new SerializablePairLongString(123,
null))
* serialize using new, deserialize using old
* value: P(123, null)
* original behaviour -> deserializeOld(serializeOld(P(123, null))) =
P(123, null)
* deserializeOld(serializeNew(P(123, null))) = P(123, null)
* Behaviour matches the original behaviour
* value: P(123, "")
* original behaviour -> deserializeOld(serializeOld(P(123, ""))) =
P(123, null)
* deserializeOld(serializeNew(P(123, ""))) = P(123, null)
* Behaviour matches the original behavior, however is incorrect
* serialize using old, deserialize using new
* value: P(123, null)
* original behaviour -> deserializeOld(serializeOld(P(123, null))) =
P(123, null)
* deserializeNew(serializeOld(P(123, null))) = P(123, "")
* Behaviour doesn't match the original behaviour
* value: P(123, "")
* original behaviour -> deserializeOld(serializeOld(P(123, ""))) =
P(123, null)
* deserializeNew(serializeOld(P(123, ""))) = P(123, "")
* Behaviour doesn't match the original behaviour, however the output
is what was actually entered by the user.
<hr>
In the second case, using the old serde means that the info whether the
string was null or empty was lost. Therefore returning null (old behavior) or
"" (new behavior) should be acceptable because the behavior was incorrect in
the first place. This only happens when the old writer has deserialized the
information, which already means that the distinction between null & empty was
already lost.
#### Release note
<hr>
##### Key changed/added classes in this PR
* `MyFoo`
* `OurBar`
* `TheirBaz`
<hr>
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- [ ] added integration tests.
- [ ] been tested in a test Druid cluster.
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