wg_database_freesize result never decreases

[vividsnow]

Hello
First of all, thanks for this project.

I'm trying to implement cache on top of whitedb, but found that even after deleting all records, wg_database_freesize result never decreases.
Is there way to estimate real free size?

[priitj]

Hi,

Short answer: it's possible, but expensive to calculate.

You can think of whitedb memory allocation as working on two levels. There are bigger chunks that hold one type of objects, such as integers and strings. When one chunk gets filled, another of the same type is allocated. This "chunk level" memory is cheap to keep track of and this is what the wg_database_freesize() reports. However, it is not necessary to free those chunks and the side effect is that the size reported by that function never decreases.

The objects inside the chunks are freed and the memory does get reused. But the information about the free objects is stored in a way that makes it expensive to add up all the available space.

If you're curious then you can look at the function wg_show_db_area_header() and the functions that it calls in Test/dbtest.c

For practical purposes the best way would be to implement bookkeeping inside the whitedb library. There are a limited number of functions that create and free objects in Db/dballoc.c.

[vividsnow]

ok, thanks