BUFFER LATCH in SQL server

A BUFFER LATCH is a protection mechanism used by SQL Server to safeguard buffer pool pages while they are being read or written. Whenever SQL Server reads a page from disk or writes a page to disk or pins page in buffer or checks page validity or modifies internal memory metadata. SQL Server places a Buffer Latch on that page.

we need Buffer Latches because multiple threads may try to simultaneously access same buffer page for readers or modifiers or flushing threads or checkpoint or Lazy writer. So, buffer latch protects in-memory page while it is being accessed. BUT unlike Locks, it has nothing to do with transactions.

Feature	BUFFER LATCH	PAGELATCH	LOCK
Protects	In-memory buffer structures	In-memory page access coordination	Logical data consistency
Location	Buffer Pool	Buffer Pool page access	Transaction engine
Purpose	Safety of memory copy of page	Avoid concurrent corruption of in-memory page	Isolation + concurrency control
Duration	Microseconds–milliseconds	Microseconds–milliseconds	Transaction duration
Appears in sys.dm_tran_locks	❌ No	❌ No	✔ Yes
Root problem when high	I/O stress / memory pressure	TempDB / hot page contention	Blocking

 Short version

Ø  Buffer Latch = Protect buffer page during I/O + internal access

Ø  Pagelatch = protect shared in-memory page access

Ø  Lock = protect logical data modifications

Below are the common buffer latch wait type

Wait Type	Meaning
BUFFERLATCH	General buffer latch wait
BUFFERLATCH_SH	Shared access to buffer
BUFFERLATCH_EX	Exclusive latch on buffer
BUFFERLATCH_UP	Update latch
PAGEIOLATCH_*	(Often seen with buffer latch during disk read)