This document provides an overview of MySQL for Linux system administrators. It discusses MySQL architecture including storage engines, memory usage, the MySQL server process, and InnoDB transaction processing. It also covers topics like backups and replication, and the agenda includes performance and capacity planning. The goal is to help system administrators understand and manage MySQL databases.

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MySQL
For
Linux
Sysadmins
Morgan
Tocker
MySQL
Community
Manager
August,
2014

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Safe
Harbor
Statement
The
following
is
intended
to
outline
our
general
product
direction.
It
is
intended
for
information
purposes
only,
and
may
not
be
incorporated
into
any
contract.
It
is
not
a
commitment
to
deliver
any
material,
code,
or
functionality,
and
should
not
be
relied
upon
in
making
purchasing
decisions.
The
development,
release,
and
timing
of
any
features
or
functionality
described
for
Oracle’s
products
remains
at
the
sole
discretion
of
Oracle.
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Program
Agenda
Introduction
MySQL
Architecture
Backup
&
Replication
Performance
&
Capacity
Planning
1
2
3
4

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The
Career
Path
to
DBA
• Start
as
a
Developer
• Start
as
a
Sysadmin
• Train
to
be
a
DBA
5
Usually either #1 or #2.
I started as a Developer
}

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Non
Exhaustive
List
of
Duties
• Backup
• Replication
• Patching
&
Upgrades
• Performance
and
Capacity
Planning
• Coaching
&
Mentoring
• Fighting
Fires
6

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Program
Agenda
Introduction
MySQL
Architecture
Backup
&
Replication
Performance
&
Capacity
Planning
1
2
3
4
2
1

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About
MySQL
• Version
numbers
are
misleading:
• 5.5
to
5.6
was
the
biggest
upgrade
in
history
• 5.6.xx
• Micro-­‐release
approximately
every
2
months.
• Fixes
bugs
and
security
vulnerabilities.
8

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About
MySQL
(cont.)
• 5.7.xx
• Current
focus
of
development.
• Release
cycle
is
2-­‐3
years.
• 5.5
and
5.6
are
under
active
support.
9

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Storage
Engines
in
MySQL
• InnoDB
(default)
• MyISAM
(previous
default)
• NDB
Cluster
• Other
11

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Memory
Usage
• Databases
like
to
allocate
large
amounts
of
memory
for
caches
• Better
to
run
with
smaller
caches
than
swap
• Kind
of
works
as
“double
buffering”
of
operating
system
caches
12

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MySQL
Server
• Single
process
of
mysqld
• Supervisor
process
is
mysqld_safe
• Each
new
MySQL
connection
consumes
a
thread
• With
the
server
maintaining
a
small
thread
cache
13

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Transaction
System
StorageCaching
SYS_TABLES
ibdata1
space0
Page Cache
A.ibd
B.ibd
C.ibd
IBUF_HEADER
IBUF_TREE
TRX_SYS
FIRST_RSEG
DICT_HDR
Data Dict.
SYS_COLUMNS
SYS_INDEXES
SYS_FIELDS
Block 1 (64 pages)
Block 2 (64 pages)
iblogfile0 iblogfile1 iblogfile2
Tables with
file_per_tableDoublewrite Buffer
BufferPool
Data Dictionary Cache
Adaptive Hash Indexes
Buffer Pool LRU
Additional Mem Pool
Log Buffer
LogGroup
Buffer Pool Flush List
In Memory
On Diskhttps://github.com/jeremycole/innodb_diagrams

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InnoDBTransaction
System
StorageCaching
SYS_TABLES
ibdata1
space0
Page Cache
A.ibd
B.ibd
C.ibd
IBUF_HEADER
IBUF_TREE
TRX_SYS
FIRST_RSEG
DICT_HDR
Data Dict.
SYS_COLUMNS
SYS_INDEXES
SYS_FIELDS
Block 1 (64 pages)
Block 2 (64 pages)
iblogfile0 iblogfile1 iblogfile2
Tables with
file_per_tableDoublewrite Buffer
BufferPool Data Dictionary Cache
Adaptive Hash Indexes
Buffer Pool LRU
Additional Mem Pool
Log Buffer LogGroup
Buffer Pool Flush List
SELECT * FROM a
WHERE id = 10;
mysqld
Not Found
Query
-­‐
Non
Cached

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InnoDBTransaction
System
StorageCaching
SYS_TABLES
ibdata1
space0
Page Cache
A.ibd
B.ibd
C.ibd
IBUF_HEADER
IBUF_TREE
TRX_SYS
FIRST_RSEG
DICT_HDR
Data Dict.
SYS_COLUMNS
SYS_INDEXES
SYS_FIELDS
Block 1 (64 pages)
Block 2 (64 pages)
iblogfile0 iblogfile1 iblogfile2
Tables with
file_per_tableDoublewrite Buffer
BufferPool Data Dictionary Cache
Adaptive Hash Indexes
Buffer Pool LRU
Additional Mem Pool
Log Buffer LogGroup
Buffer Pool Flush List
SELECT * FROM a
WHERE id = 10;
mysqld
Query
-­‐
Cached

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Update
Query
in
a
Transaction
(simplified)
InnoDB
Transaction
System
StorageCaching
SYS_TABLES
ibdata1
space0
Page Cache
A.ibd
B.ibd
C.ibd
IBUF_HEADER
IBUF_TREE
TRX_SYS
FIRST_RSEG
DICT_HDR
Data Dict.
SYS_COLUMNS
SYS_INDEXES
SYS_FIELDS
Block 1 (64 pages)
Block 2 (64 pages)
iblogfile0 iblogfile1 iblogfile2
Tables with
file_per_tableDoublewrite Buffer
BufferPool
Data Dictionary Cache
Adaptive Hash Indexes
Buffer Pool LRU
Additional Mem Pool
Log Buffer
LogGroup
Buffer Pool Flush List
UPDATE a SET col1 =
‘new’ WHERE id = 10;
mysqld
commit;

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Log
Files
• Provide
recovery.
• Only
written
to
in
regular
operation.
• Read
only
required
if
there
is
a
crash.
• Are
rewritten
over-­‐and-­‐over
again.
• Think
of
it
like
a
tank
tread.
18

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19
Program
Agenda
Introduction
MySQL
Architecture
Backup
&
Replication
Performance
&
Capacity
Planning
1
2
3
4
1
3

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Backup
(Theory)
• Cold
• Warm
• Hot
20

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Backup
Consistency
• Must
represent
a
single
point
in
time
21

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| 22
customerid name
1 Acorn Enterprises
2 First National Squirrel Bank
3 Squirrels 5000 Inc
invoiceid customerid ...
1 1 # Acorn Enterprises
2 1 # Acorn Enterprises
3 3 # Squirrels 5000 Inc
customer
invoice
itemid invoiceid Description Amount
1 1 1 hrs Professional
Services
$10
2 2 Acorn Parts $12.50
3 2 5 hrs Professional
Services
$50
4 3 Delivery Fee $17.50
5 3 Replacement
Acorn
$20
invoice_item

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| 23
customerid name
1 Acorn Enterprises
2 First National Squirrel Bank
3 Squirrels 5000 Inc
invoiceid customerid ...
1 1 # Acorn Enterprises
2 1 # Acorn Enterprises
3 3 # Squirrels 5000 Inc
customer
invoice
itemid invoiceid Description Amount
1 1 1 hrs Professional
Services
$10
2 2 Acorn Parts $12.50
3 2 5 hrs Professional
Services
$50
4 3 Delivery Fee $17.50
5 3 Replacement
Acorn
$20
invoice_item

24. Copyright
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| 24
customerid name
1 Acorn Enterprises
2 First National Squirrel Bank
3 Squirrels 5000 Inc
invoiceid customerid ...
1 1 # Acorn Enterprises
2 1 # Acorn Enterprises
3 3 # Squirrels 5000 Inc
customer
invoice
itemid invoiceid Description Amount
1 1 1 hrs Professional
Services
$10
2 2 Acorn Parts $12.50
3 2 5 hrs Professional
Services
$50
4 3 Delivery Fee $17.50
5 3 Replacement
Acorn
$20
invoice_item

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| 25
customerid name
1 Acorn Enterprises
2 First National Squirrel Bank
3 Squirrels 5000 Inc
4 Savvy Squirrel Global
invoiceid customerid ...
1 1 # Acorn Enterprises
2 1 # Acorn Enterprises
3 3 # Squirrels 5000 Inc
4 4 # Savvy Squirrels
customer
invoice
itemid invoiceid Description Amount
1 1 1 hrs Professional
Services
$10
2 2 Acorn Parts $12.50
3 2 5 hrs Professional
Services
$50
4 3 Delivery Fee $17.50
5 3 Replacement
Acorn
$20
6 4 Premium Acorn $999
invoice_item

26. Copyright
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| 26
customerid name
1 Acorn Enterprises
2 First National Squirrel Bank
3 Squirrels 5000 Inc
4 Savvy Squirrel Global
invoiceid customerid ...
1 1 # Acorn Enterprises
2 1 # Acorn Enterprises
3 3 # Squirrels 5000 Inc
4 4 # Savvy Squirrels
customer
invoice
itemid invoiceid Description Amount
1 1 1 hrs Professional
Services
$10
2 2 Acorn Parts $12.50
3 2 5 hrs Professional
Services
$50
4 3 Delivery Fee $17.50
5 3 Replacement
Acorn
$20
6 4 Premium Acorn $999
invoice_item

27. Copyright
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| 27
customerid name
1 Acorn Enterprises
2 First National Squirrel Bank
3 Squirrels 5000 Inc
4 Savvy Squirrel Global
invoiceid customerid ...
1 1 # Acorn Enterprises
2 1 # Acorn Enterprises
3 3 # Squirrels 5000 Inc
4 4 # Savvy Squirrels
customer
invoice
itemid invoiceid Description Amount
1 1 1 hrs Professional
Services
$10
2 2 Acorn Parts $12.50
3 2 5 hrs Professional
Services
$50
4 3 Delivery Fee $17.50
5 3 Replacement
Acorn
$20
6 4 Premium Acorn $999
invoice_item

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| 28
customerid name
1 Acorn Enterprises
2 First National Squirrel Bank
3 Squirrels 5000 Inc
4 Savvy Squirrel Global
invoiceid customerid ...
1 1 # Acorn Enterprises
2 1 # Acorn Enterprises
3 3 # Squirrels 5000 Inc
4 4 # Savvy Squirrels
customer
invoice
itemid invoiceid Description Amount
1 1 1 hrs Professional
Services
$10
2 2 Acorn Parts $12.50
3 2 5 hrs Professional
Services
$50
4 3 Delivery Fee $17.50
5 3 Replacement
Acorn
$20
6 4 Premium Acorn $999
invoice_item

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Backup
Methods
• mysqldump
• Is
warm
by
default.
Can
safely
be
set
hot
if
all
InnoDB.
• Logical
backup.
Slow
to
recover.
• Snapshot
Based
-­‐
i.e.
LVM
snapshot.
• Consistent
+
Hot
• May
have
higher
impact
during
snapshot
phase.
• Best
used
with
a
script
like
mylvmbackup.
29

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Backup
Methods
(cont.)
• MySQL
Enterprise
Backup
• Commercial
Tool
• Hot
with
InnoDB.
Warm
for
MyISAM
phase
• Low
Impact
30

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How
to
Decide?
• MTTR
of
logical
backups
is
much
higher.
• Most
failures
are
accidents
(either
by
DBA
or
user).
• “I
accidentally
updated
the
phone
number
of
the
wrong
customer!”
31

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Replication
• Built
in
to
MySQL
• Easy
to
setup
and
get
running
• Uses
same
port
3306
• Most
deployments
will
use
Replication
32

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Replication
Options
• Row
Format
• Statement
Based
(default)
• Row
Based
• Global
Transaction
IDs
• Semi-­‐Synchronous
• Time
delayed
33

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Program
Agenda
Introduction
MySQL
Architecture
Backup
&
Replication
Performance
&
Capacity
Planning
1
2
3
4
1
4

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Quality
of
Service
• Often
better
to
let
one
too
demanding
user
go
unserviced
than
all
users
go
unserviced
• Statement
Timeout
coming
to
MySQL
5.7.
35

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Quality
of
Service
(cont.)
• Replication
Slaves,
Hadoop
very
useful.
• Important
to
Optimize
for
Response
Time
(user
facing)
before
sub
optimizing
for
background
tasks.
36

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Configuration
Most
important
settings
• innodb_buffer_pool_size
-­‐
50-­‐80%
of
memory
• innodb_log_file_size
-­‐
up
to
4G
quite
safe
37

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Configuration
Also
Useful
• innodb_flush_method
• innodb_flush_neighbors
• innodb_io_capacity
and
innodb_lru_scan_depth
• Explained
here:
• http://www.tocker.ca/2013/09/17/what-­‐to-­‐tune-­‐in-­‐
mysql-­‐56-­‐after-­‐installation.html
38

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How
much
can
you
expect
from
config?
Versus
other
optimizations
• Optimizing
Queries
is
critical
to
performance
• SQL
is
hard
• Easy
to
write
• Hard
to
sight
check
for
performance
39

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How
to
find
slow
queries?
• Pro-­‐active:
• Design
or
review
all
schema
and
queries.
• Re-­‐active:
• Find
worst
offenders
and
suggest
improvements
to
development
staff.
40

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Realistic
Compromise
• Query
and
index
usage
changes
over
time
• You
have
to
have
tools
in
place
to
find
slow
SQL
• We
release
MySQL
Enterprise
Monitor
for
this
purpose
41

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Hardware
Choices
• Frequently
memory
is
under-­‐provisioned
• http://rhaas.blogspot.ca/2014/08/memory-­‐
matters.html
(PostgreSQL)
• http://www.tocker.ca/2013/05/10/twice-­‐as-­‐much-­‐
ram-­‐does-­‐not-­‐equal-­‐twice-­‐as-­‐fast.html
(Me;
MySQL)
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Hardware
Choices
(cont.)
• SSD
transition
is
real
• But
still
better
to
buy
more
memory
first
• Database
need
to
write
for
persistence.
Heavier
IO
requirements
than
any
other
tier
43

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Hardware
Choices
(cont.)
• More
CPUs
can
mean
more
consistent
performance
• Some
level
of
scale
up
+
scale
out
is
best:
• http://www.tocker.ca/2014/04/22/five-­‐reasons-­‐why-­‐
vertical-­‐scalability-­‐matters.html
44

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Non
Exhaustive
List
of
Duties
• Backup
• Replication
• Patching
&
Upgrades
• Performance
and
Capacity
Planning
• Coaching
&
Mentoring
• Fighting
Fires
45

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46