OnFlushCompleted should update file discardable size about titan

[yiwu-arbug]

I don't know how to fix this one, since OnFlushCompleted don't know what's the input data size for each blob file.

[JiayuZzz]

@yiwu-arbug
I think we can use output data size to get discardable_size of flushed blob file:

0. If discardable_size == 0, then discardable_size = file_size - output_size
1. if discardable_size > 0, then discardable_size = discardable_size - output_size ( for those blob file indexes that not be flushed completely in one run )

The problem is if all keys of a blob_file are deleted in memtable then we will still lose discardable_size.

[yiwu-arbug]

@wujy-cs sounds reasonable. So basically, a) mark the latest memtable id (say, M) after GC finish, b) wait till M flushed, then subtract file size by sum of output size of all memtables?

[JiayuZzz]

@yiwu-arbug
Yes,. And we can do it in OnFlushCompleted without distinguishing gc rewritten blob file and flushed blob file, since outpu_size of flushed blob file always equals to file_size.