Question: Current status of interleaved table support

[yfuruyama]

There used to be an interleaved table limitation in README, but now that limitation has been removed along with interleaved samples in PR-144.

What is the current status of the support for interleaved tables with this adapter? Can we assume that it's fully supported in this adapter?

[hengfengli]

There are some issues (active record does not support composite primary keys) with the interleaved table support so we decided to not expose it. I think the implementation is not deleted but I would not say it is fully supported.

[yfuruyama]

@hengfengli Thank you for sharing the current status. Let me ask another questions.

1. I have heard from one of users that even using composite_primary_keys have some issues to run DML on Spanner. Is there any initiative to support interleaved tables with/without such 3rd-party libraries?
2. Can we revert this change for README so that users can understand the current limitation of interleaved tables?

[hengfengli]

1. Is it an issue with this active record support? We tried to support interleaved tables without using any 3rd-party libraries. I think we would try to not rely on a 3rd-party library. CC @olavloite
2. No, I don't think so.

[yfuruyama]

1. I've heard that without using composite_primary_keys it looks like DML are not working. It looks like the parent primary key part of composite primary keys could be empty for DML.
2. Sorry, I wanted to mean that it would be better to explicitly mention in README that interleaved tables are not supported for now so that users can understand the limitation.

[olavloite]

1. I've heard that without using composite_primary_keys it looks like DML are not working. It looks like the parent primary key part of composite primary keys could be empty for DML.

That is (partly) correct:

1. The parent key was not included in DML statements, and also not in SELECT statements that fetched one row. That would however not cause a row not to be found or multiple rows to be found, as the interleaved table support was implemented in such a way that both the parent and the child key were both globally unique.
2. The problem with it was however that it meant that Spanner had to do a full table scan to fetch/update one row, as we executed a statement on only one of the key columns. A possible solution to that could have been to instruct everyone to create a unique index on the child key column. We decided against that because of the added complexity and the probability that someone would forget that and experience very bad performance.

2. Sorry, I wanted to mean that it would be better to explicitly mention in README that interleaved tables are not supported for now so that users can understand the limitation.

Sounds reasonable to me.

[yfuruyama]

Thanks @olavloite for the comments. I updated the README for current limitation: #161.

[yfuruyama]

Let me close this issue as the current status of interleaved tables support is now clear.

I have heard that @yuemori has some idea about using composite_primary_keys to fully support interleaved tables with this adapter, so let me ask him to file a new issue for that.