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TwinDB
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Put and delete entries are cached in memory until TwinDB_sync() is called or a read occurs (by calling TwinDB_get()). Then, it: | Put and delete entries are cached in memory until TwinDB_sync() is called or a read occurs (by calling TwinDB_get()). Then, it: | ||
| − | + | *1. locks the first database | |
| − | + | *2. writes to it | |
| − | + | *3. unlocks it | |
| − | + | ||
and repeats this process for the backup database. Upon startup, it checks to see if a lock is on either file. If so, it assumes that database file is corrupt and replaces it with the other. | and repeats this process for the backup database. Upon startup, it checks to see if a lock is on either file. If so, it assumes that database file is corrupt and replaces it with the other. | ||
Cons: | Cons: | ||
| − | + | * writes are 1/2 as fast | |
| − | + | * database is 2x as big | |
| − | + | ||
Pros: | Pros: | ||
| − | + | * the database cannot be corrupted | |
| − | + | * it's still *very* fast | |
| − | + | * it's free for commercial use | |
| − | + | * the size difference might not matter (current hard disks are typically over 100G, so a 500M database will still only take up less than 1% of the drive if doubled) | |
| − | + | ||
==相关链接== | ==相关链接== | ||
2010年9月26日 (日) 10:10的最后版本
[编辑] 简介
TwinDB is an embedded key/value database based on BerkeleyDB. It basically adds security from database corruption on top of the non-transactional version of BerkeleyDB. I wrote it because the transactional version of Berkeley DB is expensive ($100,000 for a commercial license).
It accomplishes this by maintaining twin BerkeleyDB databases and using "lock" files to indicate when a set of writes are in progress.
Put and delete entries are cached in memory until TwinDB_sync() is called or a read occurs (by calling TwinDB_get()). Then, it:
- 1. locks the first database
- 2. writes to it
- 3. unlocks it
and repeats this process for the backup database. Upon startup, it checks to see if a lock is on either file. If so, it assumes that database file is corrupt and replaces it with the other.
Cons:
- writes are 1/2 as fast
- database is 2x as big
Pros:
- the database cannot be corrupted
- it's still *very* fast
- it's free for commercial use
- the size difference might not matter (current hard disks are typically over 100G, so a 500M database will still only take up less than 1% of the drive if doubled)
