assertTrue(sessionPoolOptions.warnInactiveTransactions());

A Spanner object of the Client Library has a limit on the number of maximum sessions. For example the

default value of `MaxSessions` in the Java Client Library is 400. You can configure these values at the time of

Client side Database object creation by passing in the `SessionPoolOptions`. When all the sessions are checked

out of the session pool, every new transaction has to wait until a session is returned to the pool.

If a session is never returned to the pool (hence causing a session leak), the transactions will have to wait

indefinitely and your application will be blocked.

The most common reason for a session leak is that a transaction was started by the application but

never committed or rolled back. What you should do is simply call commit on the transaction at the

end of your transaction code. Spanner has two types of transactions, read only and read-write

transactions. When we perform a read in a read-write transaction we still need to commit it.

As shown in the example below, the `try-with-resources` block releases the session after it is complete.

If you don't use `try-with-resources` block, unless you explicitly call the `close()` method on all resources

such as `ResultSet` the session is not released back to the pool. If the transaction does not run within

`try-with-resources` block and if we don't close the resources explicitly, we will have a session leak.

DatabaseClient client =

spanner.getDatabaseClient(DatabaseId.of("my-project", "my-instance", "my-database"));

try (ResultSet resultSet =

client.singleUse().executeQuery(Statement.of("select col1, col2 from my_table"))) {

while (resultSet.next()) {

// use the results.

}

}

Enabled by default, the logging option shares warn logs when you have exhausted >95% of your session pool.

This could mean two things, either you need to increase the max sessions in your session pool (as the number

of queries run using the client side database object is greater than your session pool can serve) or you may

have a session leak.

To help debug which transactions may be causing this session leak, the logs will also contain stack traces of

transactions which have been running longer than expected. The logs are pushed to a destination based on

how the log exporter is configured for the host application.

``` java

final SessionPoolOptions sessionPoolOptions =

SessionPoolOptions.newBuilder().setWarnIfInactiveTransactions().build()

final Spanner spanner =

SpannerOptions.newBuilder()

.setSessionPoolOption(sessionPoolOptions)

.build()

.getService();

final DatabaseClient client = spanner.getDatabaseClient(databaseId);

When the option to automatically clean inactive transactions is enabled, the client library will automatically spot

problematic transactions that are running for extremely long periods of time (thus causing session leaks) and close them.

The session will be removed from the pool and be replaced by a new session. To dig deeper into which transactions are being

closed, you can check the logs to see the stack trace of the transactions which might be causing these leaks and further

debug them.

``` java

final SessionPoolOptions sessionPoolOptions =

SessionPoolOptions.newBuilder().setWarnAndCloseIfInactiveTransactions().build()

final Spanner spanner =

SpannerOptions.newBuilder()

.setSessionPoolOption(sessionPoolOptions)

.build()

.getService();

final DatabaseClient client = spanner.getDatabaseClient(databaseId);