If an exception that cannot be retried occurs while executing the BeginTransaction gRPC, the Spanner session pool could leak a session.
Consider the following example:
SpannerOptions.Builder builder =
SpannerOptions.newBuilder()
.setProjectId("[PROJECT]")
builder.setSessionPoolOption(
SessionPoolOptions.newBuilder()
.setMinSessions(0)
.setMaxSessions(2)
.setWriteSessionsFraction(0.0f)
.build());
Spanner spanner = builder.build().getService();
DatabaseClient client =
spanner.getDatabaseClient(DatabaseId.of("[PROJECT]", "[INSTANCE]", "[DATABASE]"));
TransactionRunner runner = client.readWriteTransaction();
long updateCount =
runner.run(
new TransactionCallable<Long>() {
@Override
public Long run(TransactionContext transaction) throws Exception {
return transaction.executeUpdate(UPDATE_STATEMENT);
}
});The above session pool will never contain a prepared transaction, as the writeSessionsFraction is set to 0. Creating a read/write transaction will therefore always require the session pool to prepare a new session. If the BeginTransaction rpc returns a non-retryable error, the error is returned to the client, but the session that is taken to be prepared by the session pool is never returned to the session pool.
If an exception that cannot be retried occurs while executing the BeginTransaction gRPC, the Spanner session pool could leak a session.
Consider the following example:
The above session pool will never contain a prepared transaction, as the writeSessionsFraction is set to 0. Creating a read/write transaction will therefore always require the session pool to prepare a new session. If the BeginTransaction rpc returns a non-retryable error, the error is returned to the client, but the session that is taken to be prepared by the session pool is never returned to the session pool.