Performance issues with POST to large containers

[ThomasJejkal]

After evaluating the POST performance of the Web Annotation Protocol server the performance issues presented in the final report could be reproduced. Furthermore, the reason for the relationship between performance decrease and container size could be identified and is cause by the following Jena code:

https://github.com/apache/jena/blob/a7ba51f67e7af819178fea9a06a6dad0415877c3/jena-core/src/main/java/org/apache/jena/rdf/model/impl/ContainerImpl.java#L181

The size() method is used in org.​apache.​jena.​rdf.​model.​impl.SeqImpl to determine the current size of the container before adding a new element. Iterating through all elements will cause a steadily slowdown of POST operations as shown in the following table:

Number of Elements in a Container	Time to add one new Element [ms]	Time to add next 10K Elements [hh:mm:ss] (approx.)
10.000	40	00:06:40
20.000	56	00:09:20
30.000	69	00:11:30
40.000	83	00:13:50
50.000	107	00:17:50
60.000	117	00:19:30
...	...	...
140.000	253	00:39:10
...	...	...
500.000	768 (est.)	02:09:40

Of course, these values will depend on the local hardware, but one should at least estimate an increase of approx. 15 ms for posting one annotation every 10.000 elements.

Currently, there seem to be two solutions:

1. Being aware of the described behaviour and prefer using small containers or containers of containers.
2. Change the implementation of the Jena repository to store sequence information elsewhere, e.g. in a relational database.