Latches are nontransactional synchronization mechanisms used to guarantee the physical consistency of a page. While rows are being inserted, updated, or deleted, only one Adaptive Server process can access the page. Latches are used for datapages and datarows locking, but not for allpages locking.
The most important distinction between a lock and a latch is duration:
A lock can persist for a long period of time: while a page is being scanned, while a disk read or network write takes place, for the duration of a statement, or for the duration of a transaction.
A latch is held only for the length of time required to insert or move a few bytes on a data page, to copy pointers, columns, or rows, or to acquire a latch on another index page.
