(PHP 4, PHP 5, PHP 7)
dba_optimize — Optimize database
$handle
)dba_optimize() optimizes the underlying database.
成功时返回 TRUE， 或者在失败时返回 FALSE。
The difference between "dba_optimize" and "dba_sync":
Use "dba_optimize" to optimize a database, which usually consists of eliminating gaps between records created by deletes.
The "dba_sync" function will synchronize the view of the database in memory and its image on the disk. As you insert records, they may be cached in memory by the underlying engine. Other processes reading from the database will not see these new records until synchronization.
Note that the internal structure of each DB that needs to access etherogeneous data in a *fast* way it is not necessarily space-optimized. So, if you add-remove-substitute keys with data having different content length, the db continues to grow, wasting space. So, it is necessary, sometimes, to re-pack the db in order to remove unused data from the db itself. But it is important to remind that, even if the file grows, the data remain optimized and - obviously - the access continues to be fast. Further information are available at dba_replace() user-contributed notes.