high disk and memory usage

[andreasbaumann]

Running updates for several months without stopping/starting (respectively using the close index
command) results in high disk usage (in our project 700 MB to 36 GB). This naturally also
increases the amount of memory needed to cache the first two levels of the leveldb structures.

[andreasbaumann]

This bug is critical, it renders the strusWebService not ready for productive environments!

[andreasbaumann]

issuing a /strus/index/close/xxx doens't solve the problem. Only restarting the strusWebSerivce.

[andreasbaumann]

This bug also happens when doing bigger inserts (like 100'000 documents). It seems calling commit
doens't do anything on the LevelDB layer to properly organize the data structure.