CDB cache

Created by: Xottab-DUTY

It looks like the engine file system doesn't flush the files immediately to disk. If the engine will be closed before the cache is flushed to disk, the cache files will be broken.

CDB cache was added in #698.

• Flush to disk immediately (ad881d60)
  • Sub-task: Rescan CDB cache folder (#709 (closed))
    • Rescan not needed, it was a bug fixed in ad881d60
• Version check (#727, #762)
• Integrity check (a0f04501)