[BEAM-12504] Make SpannerIO.ConnectTransaction wait on input signal

[baeminbo]

The current SpannerIO creates transaction at the beginning of pipeline run. This causes SpannerIO error by session not found if the pipeline runs long with ReadAll which gets ReadOperation as input .

This change introduces a delayed transaction creation. It makes a pipeline able to create Spanner transaction when it is needed (e.g. just before ReadAll).

Take a look at the code below with this change applied. It will creates a transaction session after readOperations is finished. FYI, the code will fail to compile with the current SpannerIO because CreateTransaction only accepts PBegin at the moement.

SpannerConfig config = ...

PCollection<ReadOperation> readOperations = ...

PCollectionView<Transaction> transaction = readOperations.apply(SpannerIO.createTransaction());

PCollection<Struct> users = readOperations
  .apply(SpannerIO.readAll().withSpannerConfig(config).withTransaction(transaction))

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[baeminbo]

@pabloem Can you take a look at this PR?

[pabloem]

sorry about the delay. Looking...

[aaltay]

@baeminbo - Pablo will be out of office until August. I do not know the level of urgency on this PR. If it can wait, that is fine. Otherwise, do you who else might review this?

/cc @chamikaramj

[baeminbo]

Hi, this is not urgent. Thanks!

[pabloem]

I'm back from vacation! I'll take a look now

[pabloem]

@baeminbo doesn't it make sense to use WaitCreateTransaction in all cases? So maybe just update CreateTransaction to always wait?

[baeminbo]

Hi @pabloem, I changed the code to CreateTransaction can accept PCollection so that it will wait until the input PCollection is closed. Accordingly, I updated the PR title and summary.

[pabloem]

Run Java PostCommit

[pabloem]

LGTM thanks