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2.2.2. Work execution The indexing work (done by the back end) can be executed synchronously with the transaction commit (or update operation if out of transaction), or asynchronously. 2.2.2.1. Synchronous This is the safe mode where the back end work is executed in concert with the transaction commit. Under highly concurrent environment, this can lead to throughput limitations (due to the Apache Lucene lock mechanism) and it can increase the system response time if the backend is significantly slower than the transactional process and if a lot of IO operations are involved. 2.2.2.2. Asynchronous This mode delegates the work done by the back end to a different thread. That way, throughput and response time are (to a certain extend) decorrelated from the back end performance. The drawback is that a small delay appears between the transaction commit and the index update and a small overhead is introduced to deal with thread management. It is recommended to use synchronous execution first and evaluate asynchronous execution if performance problems occur and after having set up a proper benchmark.