bug fixes

Critical: 
    - 3cdb9e0(concurrency fix: correctly lock storage)
    - a7acacf (bug fix: revert usage of TObjectLongCustomHashMap to TObjectLongHashMap)
Normal: 
    - 2e61c0f (reduce compression threshold to 1024 bytes)

Minor: 
    - c969de6 (small fix: typo in exception msg)