TODO

- compaction
  - fast : rewrite old pages and discard old partition files
    - basic impl. done
  - slow : rewrite every entries
    - not yet impl.

  - !!! compaction can only be done when other thrs are not reading old pages
    - TODO: how to ensure this

- need refactoring:
  - Page::updateLinks_ depend on mod_info_t, which is deprecated

- workdir may change while run by lib user
  - PartitionedPageIO have to handle that

- documentation: add warnings to TableOffCache
  - can be reused across transactions, but can't be shared by two or more concurrent transactions.

- ptnk_bindump seems to be broken

- Leaf::update may invoke doSplit but may cause no split 
  - update from large val -> small val fragments leaf
  - this fragmentation is invisible from sizeFree
  - doSplit when there is space left
  POSSIBLE FIX: allow doSplit without split

  -> fixed / but no test

- DupKeyLeaf::curUpdate impl.

mysql storage engine known bugs:
- entire db is lost at unknown timing

ptnk known issues list:

VERY CRITICAL
- DupKey-tree compaction is not implemented! (may result in record-loss)
- Read set

CRITICAL
- version number may exceed 64-bit
- pgid may exceed 64-bit
- handle part id > PTNK_MAX_PARTID

FIXLATER
- remove x86_64 dependency
- remove gcc dependency
- make mmap optional

PERFORMANCE ISSUES
- PartitionedPageIO impl. is very inefficient (especially PartitionedPageIO::readPage)