vindexes: ignore_nulls option for lookups

[sougou]

Fixes #6147

Signed-off-by: Sugu Sougoumarane ssougou@gmail.com

[yborovikov]

@sougou, @harshit-gangal - thank you!

i'm not very familiar with vitess internal flow, yet, looking the method names in lookup_internal.go, i got a question:

does this change cover the case when an existing non-null (key) column gets updated to a null value?

i'd imagine a change to Update method would be needed (or a change in some other file to invoke Delete instead).

[yborovikov]

fyi: our existing test case (which inserts rows with null lookup-indexed column values) is now getting:
MySql.Data.MySqlClient.MySqlException : vtgate: http://somehost:someport/: execInsertSharded: getInsertShardedRoute: lookup.Create: input has null values: row: 0, col: 1
(without adding an ignore_nulls modifier to the lookup table or any other changes - just the fresh docker image) - which is probably (please forgive me if i'm wrong) not the expected behavior for existing customers.

works fine with ignore_nulls: "true".

[yborovikov]

also, it might be worth changing the ignore_nulls parameter type to a boolean ;)

[sougou]

does this change cover the case when an existing non-null (key) column gets updated to a null value?

This should be fine because Update is implemented as a Delete->Create. This is because the lookup row can move across shards on an update: https://github.com/vitessio/vitess/blob/master/go/vt/vtgate/vindexes/lookup_internal.go#L279-L284

(without adding an ignore_nulls modifier to the lookup table or any other changes - just the fresh docker image) - which is probably (please forgive me if i'm wrong) not the expected behavior for existing customers.

This is a breaking change. But I suspect many users may actually be misled because they expect the wrong behavior. Them switching to use ignore_nulls explicitly will then work as expected.

also, it might be worth changing the ignore_nulls parameter type to a boolean ;)

This is a limitation of the vindex design. It only accepts strings. as input values.