Implementation for IncrementalFFS

Currently we use FlatFileStore in offline reindexing, using oak-run. IncrementalFFS is derived from  this FFS implementation where we create a a modified FlatFileStore having changes made in repo between 2 checkpoints. This incremental FFS can be merged with an existing FlatFileStore  creating FlatFileStore. e.g.

Lets say we have 2 checkpoints C1 and C2.

FlatFileStoreC1 is the FlatFileStore we created at C1.

IncrementalFFS-C1-C2  is incrementalFFS between C1 and C2.

Now we merge FlatFileStoreC1 with  IncrementalFFS-C1-C2 this merging results in creating a FlatFileStore which is exactly same as FlatFileStore created with checkpoint C2.

Structure of FFS:

  <path>|<node-data>

Structure of incrementalFFS:

 <path>|<node-data>|<after-checkpint>|<Operand>

Here after-checkpoint is C2 from previous example i.e. latest of checkpoints.

Operand is the operation performed on node which chenged it's state between C1-C2

The values for operand are : 

A for added
M for modified
D for deleted