feat: add gRPC-GCP channel pool as an option

[nimf]

This enables a user to opt-in for using the gRPC-GCP channel pool and configure its options.

For example:

    SpannerOptions.Builder optionsBuilder = SpannerOptions.newBuilder();

    // ...

    optionsBuilder.withGrpcGcpOptions(GcpManagedChannelOptions.newBuilder()
        .withResiliencyOptions(GcpResiliencyOptions.newBuilder()
            .setNotReadyFallback(true)
            .build())
        .build());

    Spanner spanner = optionsBuilder.build().getService();

The gRPC-GCP channel pool provides a couple resiliency improvements during some networking issues. It also provides additional channel pool metrics.

[olavloite]

In order to fix the failed lint check you need to run the following command:

mvn com.coveo:fmt-maven-plugin:format

[thiagotnunes]

We tend to use the versions specified in java-shared-dependencies. By that, I mean we usually do NOT specify version dependencies (like here), but instead rely on the versions provided by the POM import of that repository.

Could we do the same for this artifact (if it is part of any BOMs specified in the shared dependencies)?

[nimf]

It is not a part of any BOMs. If I add it to the java-shared-dependencies will all the projects depending on it automatically get grpc-gcp as a dependency or they must explicitly add it to their dependencies?

[thiagotnunes]

They must explicitly add it to their dependencies, but they won't need to specify a version. This makes sure that we are always using compatible library versions.

[olavloite]

Also, could we have a couple of tests for this feature that:

1. Verifies that the creation of sessions is actually spread across multiple channels. See SessionClientTest for the current tests for the non-gRPC-GCP channel pool solution.
2. An end-to-end test that enables this option and executes a couple of transactions to verify that enabling this option works (and continues to work in the future).

[nimf]

Also, could we have a couple of tests for this feature that:

2. An end-to-end test that enables this option and executes a couple of transactions to verify that enabling this option works (and continues to work in the future).

Added.

1. Verifies that the creation of sessions is actually spread across multiple channels. See SessionClientTest for the current tests for the non-gRPC-GCP channel pool solution.

For the GAX channel pool it is important which CHANNEL_HINT values the Spanner client uses so that every BatchCreateSession request uses different channel. And the SessionClientTest currently verifies that correct channel hints values are used. But the gRPC-GCP channel pool doesn't use channel hints. Instead these are the things required from the Spanner client to spread the sessions correctly:

• Issue N+ BatchCreateSession requests (where N is the number of channels) (this is probably already tested)
• Set up GAX with the pool size of 1
• Set up low watermark for gRPC-GCP to 0

Can you give me a hint on how it is easier to test the last two, please?

[olavloite]

@nimf I can't push any changes to your branch, so I'll attach a proposal for a test as an attachment here. Please feel free to make any changes you think would be appropriate to the test.
ChannelUsageTest.java.txt

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[nimf]

@nimf I can't push any changes to your branch, so I'll attach a proposal for a test as an attachment here. Please feel free to make any changes you think would be appropriate to the test.
ChannelUsageTest.java.txt

Wow, it's perfect! Thank you so much!

I've added you as the author, but now it requires a consent. Can you give your consent, please?

[olavloite]

@googlebot I consent.

[olavloite]

LGTM

I assume the 1.0.0 version for the grpc-gcp in the pom.xml can be removed once the shared dependencies with this dependency included has been released (?)

[nimf]

I assume the 1.0.0 version for the grpc-gcp in the pom.xml can be removed once the shared dependencies with this dependency included has been released (?)

Yes, exactly. I've already added grpc-gcp to the java-shared-dependencies but it hasn't been released yet.