1. A Day in the Life of a Row Eddie Wuerch, mcm
Salesforce Marketing Cloud

2. Hi! I’m Eddie :) SQL Server since 6.5 Microsoft Certified Master
Enterprise Architect - Salesforce Marketing Cloud
trillions of rows … 10s billions tx/day … PBs data & indexes … 24x7, no downtimes

3. The Three ‘C’s of Performance
Capacity
Configuration
Code
Disk Performance
Memory Capacity
Disk Performance
Disk Allocation Contention
Scans
Hotspotting
Insert/Update/Delete Metadata Contention
TempDB Abuse

4. The Page – 8KB Page header –page metadata Page ID Next Page ID
Page header – 96 bytes
Page header –page metadata
Page ID
Next Page ID
Previous Page ID
Owning object ID
Index ID
Index level
Free space on page
Next row offset
…other stuff
Page row / index / bitmap / BLOB data – starts at byte 97
Row-offset table – starts at last byte, moves backwards
Data page (8KB)

5. First Extent (8 pages – 64KB)
Data File Structure
The base unit of data storage is called a page.
All pages are 8KB (8192 bytes)
Pages are organized into 8-page extents of 64KB
Page 0
Head
Page 0
Page 1
Page 1
PFS
Page 2
Page 2
GAM
Page 3
SGAM
Page 3
Page 4
Page 5
Page 6
Page 6
DCM
Page 7
BCM
Page 7
Page 8
Page 9*
Page 10
Page 11 …
Page 15
First Extent (8 pages – 64KB)

6. Bitmap Metadata Pages 8,096 bytes = 64,768 bits
GAM, SGAM, BCM, DCM, IAM, ……..
96b Header …
P.0
P.1
P.2
P.3
P.4
P.5
P.6
P.7
P.8
P.9
P.10
P.11
P.12
P.13
P.14
P.15
P.16
P.17
P.18
P.19
P.20
P.21
P.22
P.23
P.24
P.25
P.26
P.27 …
First Extent
Second Extent ….
8,096 bytes = 64,768 bits
1 bit/extent = 64,768 extents
64,768 extents * 64KB/extent = ~4GB of disk space per single GAM

7. Some Metadata Page Types
Page 2: GAM – Global Allocation Map
0 = Extent is allocated
1 = Extent is free
Page 3: SGAM – Shared Global Allocation Map
0 = Extent is not mixed, or is fully-allocated mixed extent
1 = Extent is shared (Mixed Extent) with at least 1 free page
Page 6: DCM – Diff Change Map
0 = Extent has not changed since last full backup
1 = Extent has changed since last full; include in next diff backup
Page 7: BCM – Bulk Change Map
1 = Extent contains minimally-logged operations awaiting log backup
IAM – Index Allocation Map (1 per index per GAM segment)
1 = Extent holds at least one page for this index

8. More Metadata Page 1: PFS – Page Free Space – One byte per page
Bits 0 – 2: % Full
000: 0%
001: 1-50%
010: 51-80%
011: 81-95%
100: 96%+
Bit 3: Has Ghosts
Bit 4: Is IAM
Bit 5: Is in Mixed Extent
Bit 6: Is Allocated
Each PFS page covers the next 8088 pages.

9. Page#
1 = PFS
2 = GAM
3 = SGAM
6 = DCM
7 = BCM
Demo Time!

10. Query Memory Allocation
All Server Memory
Allocated to SQL Server
(sp_configure)
Buffer Pool – data cache, plan cache,
Query working memory
Query memory target
(75% of BPool)

11. Query Memory Allocation
Small Semaphore
(Cost < 3,
mem req < 5MB)
High
Query 1
Cost 35,
Req. 25MB
Medium
Low
High
Large Semaphore
(Everything else)
Cost
1-9
Resource Semaphores
(Memory grant queues)
Available Query Memory
Query 2
Cost 15,
Req. 5MB
Medium
Low
Query 2
Cost 15,
Req. 5MB
RESOURCE_SEMAPHORE
Query 1
Cost 35,
Req. 25MB
High
Cost
10-99
Medium
Query 3
Cost 275,
Req. 150MB
Low
Query 5
Cost 275,
Req. 150MB
Query 3
Cost 275,
Req. 150MB
High
Cost
Medium
Low
Query 4
Cost 2500,
Req. 25MB
Query 4
Cost 2500,
Req. 25MB
High
Cost
Medium
Low
Query 5
Cost 275,
Req. 150MB
High
Cost
10000+
Medium
Low

12. Thank you for attending!
Eddie Wuerch