feat: add support for tagging to Connection API

[olavloite]

Adds support for tagging in the Connection API. This is needed to support tagging in the JDBC driver.

This is a binary breaking change, as it adds 4 methods to the Connection interface. That interface is marked as @InternalApi and warns that it may make breaking changes without prior notice.

[yoshi-code-bot]

Some suggestions could not be made:

• google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/Connection.java
  • lines 38-38

[thiagotnunes]

How will this behave if the user never set a transaction tag?

[olavloite]

It is nullable, so that is not a problem. It is verified by this test case.

[thiagotnunes]

Out of curiosity, could we prevent the calling of this for a COMMIT? The user should not be able to do a statement tag in that case.

[olavloite]

Good question. We can't prevent it before the COMMIT, but we can throw an exception if COMMIT is called after a statement tag has been set, and I think that makes sense as we are quite strict in checking the order of other statements (e.g. you are only allowed to get a commit timestamp if you actually committed etc.).

[olavloite]

I've changed the implementation to check for this, and to throw an error if the application tries to set a statement tag for a COMMIT or ROLLBACK statement. This change also adds a change relating to DML batches: DML batches can only include one statement tag, as the statements are sent as one ExecuteBatchDmlRequest, which only allows one statement tag. This statement tag must be set before calling START BATCH DML, e.g.

SET STATEMENT_TAG = 'tag-1';
START BATCH DML;
INSERT INTO Singers (SingerId, Name) VALUES (1, 'Morrison');
INSERT INTO Singers (SingerId, Name) VALUES (2, 'Pieterson');
RUN BATCH;

[codecov]

Codecov Report

Merging #623 (0868a05) into master (004c5d7) will increase coverage by 0.17%.
The diff coverage is 86.90%.

❗ Current head 0868a05 differs from pull request most recent head df0b11d. Consider uploading reports for the commit df0b11d to get more accurate results

@@             Coverage Diff              @@
##             master     #623      +/-   ##
============================================
+ Coverage     85.06%   85.23%   +0.17%     
- Complexity     2585     2687     +102     
============================================
  Files           143      155      +12     
  Lines         14130    14531     +401     
  Branches       1368     1376       +8     
============================================
+ Hits          12019    12386     +367     
- Misses         1540     1570      +30     
- Partials        571      575       +4     

Impacted Files	Coverage Δ
...a/com/google/cloud/spanner/SessionPoolOptions.java	69.53% <ø> (-0.79%)	⬇️
.../java/com/google/cloud/spanner/SpannerOptions.java	89.50% <ø> (-0.04%)	⬇️
...a/com/google/cloud/spanner/TransactionManager.java	100.00% <ø> (ø)
...spanner/admin/database/v1/DatabaseAdminClient.java	87.96% <ø> (+4.74%)	⬆️
...anner/admin/database/v1/DatabaseAdminSettings.java	15.94% <ø> (ø)
...nner/admin/database/v1/stub/DatabaseAdminStub.java	3.70% <ø> (ø)
...in/database/v1/stub/DatabaseAdminStubSettings.java	93.45% <ø> (-0.10%)	⬇️
...base/v1/stub/GrpcDatabaseAdminCallableFactory.java	50.00% <ø> (ø)
.../admin/database/v1/stub/GrpcDatabaseAdminStub.java	97.60% <ø> (+0.29%)	⬆️
...spanner/admin/instance/v1/InstanceAdminClient.java	82.99% <ø> (+3.85%)	⬆️
... and 122 more

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[olavloite]

@thiagotnunes Would you mind taking a final look before I merge? I've rebased on master and realigned with the last choice that were made for tagging in the client library. Also: This is a binary breaking change as it adds methods to the Connection interface. Do we need a version bump for this?