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Sessions must only execute one Transaction at a time #464
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api: spanner
Issues related to the googleapis/google-cloud-cpp-spanner API.
priority: p1
Medium priority. Will be fixed prior to next release.
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type: bug
Error or flaw in code with unintended results or allowing sub-optimal usage patterns.
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`Transaction` now has a `SessionHolder` which is populated on-demand during the first operation involving that `Transaction`. The session is (normally) returned to the pool it was allocated from when the `Transaction` is destroyed, but in the interim it will not be used by any other `Transaction`. - `Transaction::Visit` passes a reference to its `SessionHolder` to its functor. These are usually `ConnectionImpl` methods, which now use the session a `Transaction` already holds, or get a new session from the pool if needed. - For Partition Read/Query cases: - Allow constructing a `Transaction` with session and transaction IDs. - Remove session from *Params structs (fixes #445). - Partitioned `Transactions` do not return their sessions to the pool, nor do the `PartitionRead` or `PartitionQuery` operations that created them. - Update tests; add a matcher to check the `Transaction` session and transaction IDs. Fixes #464 Fixes #445
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…ud-cpp-spanner#465) `Transaction` now has a `SessionHolder` which is populated on-demand during the first operation involving that `Transaction`. The session is (normally) returned to the pool it was allocated from when the `Transaction` is destroyed, but in the interim it will not be used by any other `Transaction`. - `Transaction::Visit` passes a reference to its `SessionHolder` to its functor. These are usually `ConnectionImpl` methods, which now use the session a `Transaction` already holds, or get a new session from the pool if needed. - For Partition Read/Query cases: - Allow constructing a `Transaction` with session and transaction IDs. - Remove session from *Params structs (fixes googleapis/google-cloud-cpp-spanner#445). - Partitioned `Transactions` do not return their sessions to the pool, nor do the `PartitionRead` or `PartitionQuery` operations that created them. - Update tests; add a matcher to check the `Transaction` session and transaction IDs. Fixes googleapis/google-cloud-cpp-spanner#464 Fixes googleapis/google-cloud-cpp-spanner#445
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Sessions can only execute one transaction at a time (as stated here and elsewhere). However, our current implementation does not ensure that. For each operation (call on
Client), theConnectionImpltakes aSessionfrom the pool, makes the RPC, then returns theSessionto the pool. The pool re-usesSessions in LIFO order. So, as long as the calls to theConnectionImpluse the sameTransactionrepeatedly, we will get the sameSession, but in a multi-threaded program that may not be the case.The text was updated successfully, but these errors were encountered: