feat: support getting the commit timestamp of a transaction or statement #52
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Cloud Spanner returns the commit timestamp of a read/write transaction as a part of the commit response. This PR adds support for getting that timestamp in two ways: 1. Through a CommitTimestamp() method on the SpannerConn interface. 2. Through the SHOW VARIABLE COMMIT_TIMESTAMP client side statement.
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| } { | ||
| c.commitTs = test.wantValue | ||
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| it, err := s.ShowCommitTimestamp(ctx, c, "", nil) |
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this commit timestamp is from the previous successful txn, right?
| }, | ||
| retryAborts: c.retryAborts, | ||
| } | ||
| c.commitTs = nil |
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why do we clear commitTs here?
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The commit timestamp is cleared when a new transaction is started to avoid any confusion regarding whether the commit timestamp is related to the current transaction or the one before. So if you try to get the commit timestamp while in a transaction that has not yet committed, you will get an error or NULL instead of the commit timestamp of the previous transaction.
This is also consistent with the behavior of the JDBC driver.
| if err != nil { | ||
| t.Fatalf("failed to get a connection: %v", err) | ||
| } | ||
| if _, err := conn.ExecContext(ctx, testutil.UpdateBarSetFoo); err != nil { |
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this will do an autocommit, right?
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Yes, that is correct. If you execute an update (or any other statement) on a connection that has no active transaction, the statement will be executed in autocommit mode. That means that:
- Update statements will automatically begin an implicit read/write transaction and commit that transaction directly after the update statement if the update was successful.
- Queries will automatically use a single-use read-only transaction, as that is the most efficient way of executing a single query.
Cloud Spanner returns the commit timestamp of a read/write transaction as a part of the commit response.
This PR adds support for getting that timestamp in two ways: