difference between Checkpoint and Lazy Writer

 difference between Checkpoint and Lazy Writer

Row	Checkpoint	Lazy writer
1	Checkpoint is used by sql engine to keep database recovery time in check	Lazy writer is used by SQL engine only to make sure there is enough memory left in sql buffer pool to accommodate new pages
2	Check point always mark entry in T-log before it executes either sql engine or manually	Lazy writer doesn’t mark any entry in T-log
3	To check occurrence of checkpoint , we can use below query select * from ::fn_dblog(null,null) WHERE [Operation] like ‘%CKPT’	To check occurrence of lazy writer we can use performance monitor SQL Server Buffer Manager Lazy writes/sec
4	Checkpoint only check if page is dirty or not	Lazy writer clears any page from memory when it satisfies all of 3 conditions. 1.      Memory is required by any object and available memory is full 2.      Cost factor of page is zero 3.      Page is not currently reference by any connection
5	Checkpoint is affected by two parameters 1.      Checkpoint duration: is how long the checkpoint can run for. 2.      Recovery interval: affects how often it runs.	Lazy writer is affected by 1.      Memory pressure 2.      Reference counter of page in memory
6	Check point should not be very low , it can cause increasing recovery time of database	No. of times lazy writer is executing per second should always be low else it will show memory pressure
7	Checkpoint will run as per defined frequency	No memory pressure, no lazy writer
8	Checkpoint tries to write as many pages as fast as possible	Lazy writer tries to write as few as necessary
9	checkpoint process does not put the buffer page back on the free list	Lazy writer scans the buffer cache and reclaim unused pages and put it n free list
10	We can find last run entry of checkpoint in Boot page	Lazy writer doesn’t update boot page
11	Checkpoint can be executed by user manually or by SQL engine	Lazy writer cant be controlled by user
12	It keeps no. of dirty pages in memory to minimum	It helps to reduce paging
13	Auto frequency can be controlled using recovery interval in sp_configure	Works only @ memory pressure , It uses clock algorithm for cleaning buffer cache
14	It will be automatically executed before every sql statement which requires consistent view of database to perform task like (Alter, backup, checkdb, snapshot …..)	It kicks pages out of memory when reference counter of page reaches to zero
15	Command : Checkpoint	No command available
16	It comes in picture to find min lsn whenever t-log truncates	No entry in T-log
17	Checkpoint is affected by Database recovery model	Lazy writer doesn’t get impacted with recovery model of database
18	To get checkpoint entry in error log DBCC TRACEON(3502, -1)	Not Applied
19	Members of the SYSADMIN, DB_OWNER and DB_BACKUPOPERATOR can execute checkpoint maually	Not Applied