This document discusses server memory and latching in SQL Server. It provides information on memory clerks, committed memory, working sets, and stolen memory. It also covers the different types of latches in SQL Server like buffer, page, transaction, and other latches. Details are given on latch modes and how to analyze latch wait times and classes using dynamic management views.

2. Server Memory

5. Committed Memory = RAM
Working Set(100%)
Working Set (30%)
Memory paged out
(Pagefile)

6. Committed Memory = RAM
Working Set(100%)
Working Set (30%)
This is BAD!!!
660338 2201296
http://support.microsoft.com/kb/918483

9. Target
Target

10. Access
Manager
Buffer
Manager
Memory Disk

15. SELECT
type, memory_node_id, single_pages_kb
FROM sys.dm_os_memory_clerks

16. DBCC MEMORYSTATUS

17. Server Memory
(Physical Memory)
MemClerkMemClerkMemClerkMemClerkMemClerk
Compilation Procedure Cache

18. MemClerk
MemClerk
MemClerk
MemClerk
SPA MPA VM SM
sys.dm_os_memory_clerks
Stolen “Memory To Leave” (MTL)

22. Stolen Memory

28. sys.dm_os_memory_clerks
sys.dm_os_memory_cache_counters
sys.dm_os_memory_cache_hash_tables
sys.dm_os_memory_pools

29. Server Memory
(Physical Memory)
Buffer PoolStolen “MemToLeave”
MemClerkMemClerkMemClerkMemClerkMemClerk

30. Server Memory
(Physical Memory)
MemClerkMemClerkMemClerkMemClerkMemClerk
Procedure Cache
SQL CLR
Buffer PoolStolen “MemToLeave”

31. SQL OS
Memory Management
Thread Scheduling

35. You will see latched in…

36. OTHER LATCH
LATCH_NL
LATCH_KP
LATCH_SH
LATCH_UP
LATCH_EX
LATCH_DT
Braekdown of Latch Waits
BUFFER LATCH
PAGELATCH_NL
PAGELATCH_KP
PAGELATCH_SH
PAGELATCH_UP
PAGELATCH_EX
PAGELATCH_DT
PAGEIOLATCH_NL
PAGEIOLATCH_KP
PAGEIOLATCH_SH
PAGEIOLATCH_UP
PAGEIOLATCH_EX
PAGEIOLATCH_DT
TRANSACTION LATCH
TRAN_MARKLATCH_NL
TRAN_MARKLATCH_KP
TRAN_MARKLATCH_SH
TRAN_MARKLATCH_UP
TRAN_MARKLATCH_EX
TRAN_MARKLATCH_DT
Used for
synchronization of
commits with
marked transactions
The breakdown of
these is in
sys.dm_os_latch_stats

37. +0
Ok, but what is it really?
+8
+16
+24 class
count
owner
waiters List of Waiters
Task Address of Owner
This is the latch
Latch Class (latch id)
Num KP Stuff Spin Wait DT EX UPNum SH
0123453563 111236
Count of KP
Latches
Count of SH
Latches
Superlatch and
other stuff
spinlock Waiters
exist
DT Latch
held
EX Latch
held
UP Latch
held
x64 C++ Class

38. KP SH UP EX DT
KP Y Y Y Y N
SH Y Y Y N N
UP Y Y N N N
EX Y N N N N
DT N N N N N
Y turns N
if waiters
Mode
Not always
FIFO

39. The BUFFER (BUF) latch
BUF
SH for
Reading
UP and EX for
writing
KP for
traversing
DT for freeing
PAGELATCH_XX or
PAGEIOLATCH_XX
Buffer latch in
AM
PAGE (in cache)
BUF_ONLRU 0x000001
BUF_DIRTY 0x000002
BUF_IO 0x000004
BUF_HASHED 0x000008
BUF_READ 0x000400
BUF_IOERR 0x000800
bpage
bpageno
bstat
blatch
blog
m_headerversion
m_page_id
ptr
value
Latch
Class

43. Could be an issue when in the seconds range
Not always a high count for a problem
Are latched causing you problems
PAGEIOLATCH waits = I/O Bottleneck
High BUF latch mean hot pages
Non-BUF latch waits depend on the latch class
Latch Timeouts
Unless a bug it is usually allocation pages (and usually tempdb)
Could be system table pages for a DDL
Find out the “hot” class and see if one of generally know issues
This is just bad no matter what type (5 minute wait!)