Introduction to SQL Server Memory Management - for the DBA

MemoryManagementSQLServerExploration

byiKosmikGurukulam

www.sqlserverapp.com

• SQL Server dynamically allocates &frees memory

• No need to explicitly configure it


Then, why worryabout memorymanagement?


Becausethere is aVILLAIN!

Yes, Disk I/O!

I/O reads/writes arethe one of most

resource intensive!


M E M OR YM E M OR YU S A G EU S A G E

I / OI / OC OU N TC OU N T

SQL Server needs to balance these twofactors


M E M OR YM E M OR YU S A G EU S A G E

I / OI / OC OU N TC OU N T

Storing too much in memory also bloatsup SQL Server's memory usage


M E M OR YM E M OR YU S A G EU S A G E I / OI / O

C OU N TC OU N T

Reducing memory use willrequire more frequent disk

I/O! www.sqlserverapp.com

BUFFERMANAGEMENT

Key to achieving I/Oefficiency


BUFFER

8KB page inmemory


C O M P O N E N T SC O M P O N E N T S I NI NB U F F E RB U F F E R M A N A G E M E N TM A N A G E M E N T

BUFFER CACHE /POOL

BUFFERMANAGER


C O M P O N E N T SC O M P O N E N T S I NI NB U F F E RB U F F E R M A N A G E M E N TM A N A G E M E N T

BUFFER CACHE /POOL

Consists of 8 KB pageswww.sqlserverapp.com

H O WH O W D O E SD O E S I TI T O P E R A T E ?O P E R A T E ?

BUFFER CACHE /POOL DISK

Page is read into pool when needed

?


H O WH O W M U C HM U C H M E M O R YM E M O R Y I SI SU S E DU S E D B YB Y T H ET H E B U F F E RB U F F E R

C A C H E ?C A C H E ?


It makes sense to understand SQLServer's memory usage first


HOW DOES SQL SERVER USESYSTEM MEMORY?

SQL Serverreserves some

memory from thesystem for itspotential usage

TARGET MEMORY

SQL Server usesonly what it

actually needs atthat point in time

COMMITTED MEMORY


Q U E R Y I N GQ U E R Y I N G F O RF O R I T !I T !

SELECTcounter_name AS "STATISTIC NAME",(cntr_value/ (1024)) AS "MEMORY VALUE (MB)"FROMsys.dm_os_performance_countersWHEREcounter_nameIN ('Total Server Memory (KB)', 'Target Server Memory (KB)')


o ro r y o uy o u c o u l dc o u l d a l s oa l s o t r yt r y t h i st h i sq u e r y !q u e r y !

SELECTcommitted_kb / (1024),committed_target_kb / (1024*1024)FROMsys.dm_os_sys_info


H O WH O W D O E SD O E S S Q LS Q L S E R V E RS E R V E R U S EU S ES Y S T E MS Y S T E M M E M O R Y ?M E M O R Y ?

TARGETMEMORY

COMMITTEDMEMORY

Ramp Up


Interaction of Buffer Manager

BU F F E RBU F F E RM A N A G E RM A N A G E R

R E S OU R C ER E S OU R C EM A N A G E RM A N A G E R

DA T A BA S EDA T A BA S EM A N A G E RM A N A G E R

L OGL OGM A N A G E RM A N A G E R

Memoryusage

low-levelfile I/O

Write-aheadlogging


Information about the pages in theBuffer Pool

sys.dm_os_buffer_descriptors


ALLOCATION UNIT

Some concepts related tosys.dm_os_buffer_descriptors explained

Types/Categories of data stored in pages

3 TYPES

IN_ROW_DATA

ROW_OVERFLOW_DATA

LOB_DATA

Data in the row

When data exceeds8060 bytes

To store LOB datatype


SELECTCOUNT(*) AS number_of_pages_cached,((COUNT(*) * 8.0) / 1024) AScache_usage_in_mb,CASE

database_idWHEN 32767

THEN 'ResourceDb'ELSE DB_NAME(database_id)

END AS Database_nameFROM sys.dm_os_buffer_descriptorsGROUP BY DB_NAME(database_id) , database_idORDER BY cached_pages_count DESC;

Keeping track of pages in the Buffer Pool


TORN PAGEPROTECTION

Data Integrity Protection Mechanisms

CHECKSUMPROTECTION

2 bits to validate dataintegrity

If power failure duringdisk write corrupts data,this may not protect the

integrity always.

But this method is lessresource-intensive

Calculates checksum basedon whole data

Costlier, i.e. more resourceintensive

Is a more reliable way tocatch data integrity issues


Hope you enjoyed the slides!

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Introduction to SQL Server Memory Management - for the DBA

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