JDBC driver pausing between tranactions

A few weeks ago, a JDBC driver started processing slower and often queues up. Tracing shows that the biggest pause is in between transactions. It is about a one second delay:

[02/26/16 15:20:00.334]:IDV2PSHR ST:End transaction.
[02/26/16 15:20:01.391]:IDV2PSHR ST:Start transaction.

[02/26/16 15:20:01.484]:IDV2PSHR ST:End transaction.
[02/26/16 15:20:02.897]:IDV2PSHR ST:Start transaction.

[02/26/16 15:20:03.990]:IDV2PSHR ST:End transaction.
[02/26/16 15:20:05.011]:IDV2PSHR ST:Start transaction.

Once the transaction kicks off, it is fast. But why the one second delay between transactions?

IDM: 4.5.1