db-08: a day in the life of a type ii record richard banville progress fellow

DB-08: A Day in the Life of a Type II Record

Richard BanvilleProgress Fellow

2 DB-08: A Day in the Life of a Type II Record© 2005 Progress Software Corporation

Agenda

Update a record Details Details Details


Major Shared-Memory Structures

Buffer pool (-B)

Lock Table (-L)

BI Buffers (-bibufs)

AI Buffers (-aibufs)

Transaction Table (-n)

Usrctl (-n)

Srvctl (-Mn)

Object Cache (-omcache)


DO TRANSACTION: FIND customer WHERE

cust.name = “Dopey”. cust.name = “Smarty” cust.city = “Orlando” cust.state = “FL”.END.

A Simple Program

Begin Transaction.

Find Index Entry via chosen index

Lock & Retrieve record




A Simple Program

Update record buffer w/changed fields

Make any index changes

Save record changes




A Simple Program

Commit the updates

Release or downgrade locks


Details Part I

Getting the Record

Begin Transaction.

Find Index Entry via chosen index

Lock & Retrieve record


Start Transaction

Acquire a transaction entry Begin note deferred

Transaction Table (-n)Usrctl (-n)

User Id 9Trans Id 2433405


Finding the Record

Lookup record by area/rowid Rowid stored in index

– Associates known value with rowid

– Know values are ordered within index Language picks index

– Choice based on statement For fast access

– have index that matches predicate


Index Entry

An index entry consists of two parts:–key (one or more components)

– rowid of the record containing the key

Key Component(s)

Name Rec-Id

Bashful 256

Doc 3341

Dopey 9794

Grumpy 9806

Happy 9876

Sleepy 7776

Sneezy 512

Key Component(s)

Cust-Num Rec-Id

100 512

101 7776

102 3341

103 9876

104 9794

105 9806

106 256


Block’s DBKEY Type Chain Backup Ctr

Next DBKEY in Chain Block Update Counter

Top Reserved

Free Space

o o o

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Num Entries

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B-tree LayoutBlock’s DBKEY Type Chain Backup Ctr


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root

internal

leaf



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records



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Num Entries

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Dummy Entry . . .

Need Area & Root Block to start traversal

(Name Index)


Disk Storage Files

Storage Areas

Schema Area Area 7 Area 8

Ext

ent

Ext

ent

Ext

ent

Ext

ent

Ext

ent

Ext

ent

Ext

ent

Ext

ent

Ext

ent

Ta

ble

A

Ta

ble

B

Cu

st

Tb

l

Ta

ble

D

Ind

ex

A-1

Ind

ex

B-1

Na

me

Id

x

Cu

st#

Id

x

SR

ep

Id

x

Ind

ex

D-1

Ind

ex

D-2

Logical

Physical

Lan

gu

ages

Sto

rage E

ng

ine


Disk Storage Files

Storage Areas and Object Mapping

Schema Area Area 7 Area 8

Ext

ent

Ext

ent

Ext

ent

Ext

ent

Ext

ent

Ext

ent

Ext

ent

Ext

ent

Ext

ent

Ta

ble

A

Ta

ble

B

Cu

st

Tb

l

Ta

ble

D

Ind

ex

A-1

Ind

ex

B-1

Na

me

Id

x

Cu

st#

Id

x

SR

ep

Id

x

Ind

ex

D-1

Ind

ex

D-2

Logical

Physical

Mapping

Lan

gu

ages

Sto

rage E

ng

ine


Object Mapping Cache

replacing

Has

h T

able

LRU Chain “oldest”“newest”

aging

Area 6 Area 7 Area 8 Area 9

T1 I1 T3 I3 T2 I2 T4 I4

Array of cache entries (unordered)

Each entry contains area info & root block


Performance (omlru simplified)

replacing

Has

h T

able


aging

Omlru avoidance when –omsize proper

Area 6 Area 7 Area 8 Area 9

T1 I1 T3 I3 T2 I2 T4 I4

Find I2/T2Find I1/T1

Find I3/T3Find I2 …Find I1/T1


We know the Index’s area

We know the rowid of the index root block

Let’s find it so we can traverse the index


Find Buffer in Buffer Pool

replacing

Has

h T

able

(-h

ash

)


aging

M M M M

M MM M

Checkpoint Queue M MM M

Page Writer Queue

database

Array of (–B) buffer pool entries (unordered)

May need to flush data on page-in (if APW not @ peak performance)


Effect of -Bp

replacing

Has

h T

able

(-h

ash

)


aging

M M M M

User 1 –Bp LRU Chain

User 2 –Bp LRU Chain




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Find the “Dopey” EntryBlock’s DBKEY Type Chain Backup Ctr


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Dummy Entry . . .

root

internal

leaf



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records



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Compression effects number of blocks traversed


Free List

Active & Queued (Waiting) Lock Entries

HashTable

(-lkhash)

The Lock Table (-L)

XX SQSQ SQSQ SQSQ SQSQ

Row-id

Table-id

Owner

Lock State

Next Pointer

Lock Table Entry

SS

XX

Need to share lock the record (even though the record wasn’t located yet!)

(9794)

(1)

(Shared)

(User Id 9)


We know the Record’s rowid

In the interest of time, assume we’ve done the object mapping and attempted the

lookup in the buffer pool

Let’s go get the record


Reading a Record from Disk

* 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0

Block numbers1 to 8,388,608

Row numbers0 to 255

ROWID

prostrct list <dbname>: d “Customer":8,64 x_7.d1 f 384d “Customer":8,64 x_7.d2 f 3200d “Customer":8,64 x_7.d3

Looking for ROWID 9794, Table 1, Area 8

Find _Area where _Area-number = 8.

Display _Area-recbits _Area-Blocksize. 6 8192


Reading a Record from Disk

Find _Area where _Area-number = 8.

Display _Area-recbits _Area-Blocksize.

prostrct list <dbname>: d “Customer":8,64 x_7.d1 f 384d “Customer":8,64 x_7.d2 f 3200d “Customer":8,64 x_7.d3

Looking for ROWID 9794, Table 1, Area 8

6 8192

* 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0

Block numbers1 to 33,554,432

Row numbers0 to 63

ROWID 9794

* 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 1 0 0 1 0 0 0 0 1 0

Block: 153 Row: 2


Get the Record



Free SpaceFreeDirs. Rec 0 Offset Rec 1 Offset

Rec 2 Offset Rec n Offset

NumDirs.

Free Space

Used Data Space

Record 0

Record 1

Record 1





NumDirs.

Free Space

Used Data Space

Record 0

Record 1

Record 1

Language Record Buffer

Find the record and assemble all the pieces.Rowid 9794

Rowid 2828

Row 2 in Block 153 of area 8


Details Part II

Perform Updates

Update record buffer w/changed fields

Make any index changes

Save record changes


Update Fields in Record Buffer

New row is larger than original– Field values stored variable size

Need more space– We can handle it

new

original


State Name


Free List (-L)


HashTable

(-lkhash)

Upgrade the Lock to EX


Row-id

Table-id

Owner

Lock State

Next Pointer

LockTableEntry

SS

XX

(9794)

(1)SS


Free List (-L)


HashTable

(-lkhash)

Lock Conflict!


SS

XX

XQXQ

Queued entry - We must wait(Watch out for deadlock!)

(-lkwtmo)


Free List (-L)


HashTable

(-lkhash)

Now We Got It


SS

XX

XQXQXX


Key Component(s)

Name Rec-Id

Bashful 256

Doc 3341

Dopey 9794

Grumpy 9806

Happy 9876

Sleepy 7776

Sneezy 512

Non-unique Key

Updating an Index Entry

Key Component(s)

Name Rec-Id

Bashful 256

Doc 3341

Dopey 9794

Grumpy 9806

Happy 9876

Sleepy 7776

Smarty 9794

Sneezy 512

Non-unique Key

“Dopey” goes “Smarty”

Key Component(s)

Name Rec-Id

Bashful 256

Doc 3341

Dopey -2433405

Grumpy 9806

Happy 9876

Sleepy 7776

Smarty 9794

Sneezy 512

Unique Key


Update the Record Blocks





NumDirs.

Free Space

Used Data Space

Record 0

Record 1

Record 1





NumDirs.

Free Space

Used Data Space

Record 0

Record 1

Record 1


All buffer pool actions replayedRowid 9794

Rowid 2828

Reallocate space fragment by fragment

OOPs, out of space!


Need Space?

200200 300300 400400 200200

Record block free chain for Customer table

CustObjectBlock

CustObjectBlock

4K4K 2K2K 8K8K 8K8K

Record block free chain for Order table

OrderObjectBlock

OrderObjectBlock

Objects are selfish with their space allocation chains


Need Space?

200200 300300 400400 200200


CustObjectBlock

CustObjectBlock

Blocks on RM free chain governed by Record Packing Factor

Records/Block, Create Limit (75/150), Toss Limit (150/300)

Blocks checked, recycled or tossed is limited (internal boundaries)

Example: Need 200 bytes

Toss

Recycle Take/ Toss


Need Space?

200200 300300 400400 200200


CustObjectBlock

CustObjectBlock

Blocks on RM free chain governed by Record Packing Factor

Records/Block, Create Limit (75/150), Toss Limit (150/300)

Blocks checked, recycled or tossed is limited (internal boundaries)

Example: Need 300 bytes

Toss Toss

Recycle


Cluster Size Matters

200200 300300 400400 200200

Record block free chain for Customer Table

CustObjectBlock

CustObjectBlock 8K8K 8K8K 8K8K 8K8K 8K8K 8K8K 8K8K

AreaControlObject

AreaControlObject

8K8K8K8K8K8K8K8K8K8K8K8K8K8K8K8K





Area Cluster Free Chain


Cluster Size Matters

200200 300300 400400 200200

Record block free chain for Customer Table

CustObjectBlock

CustObjectBlock 8K8K 8K8K 8K8K 8K8K 8K8K 8K8K 8K8K

AreaControlObject

AreaControlObject





Area Cluster Free ChainCluster free chain empty? Raise area HWM or extend area.


Connect All Fragments





NumDirs.

Free Space

Used Data Space

Record 0

Record 1

Record 1





NumDirs.

Free Space

Used Data Space

Record 0

Record 1

Record 1


Rowid 9794

Rowid 2828





NumDirs.

Free Space

Used Data Space

Record 0

Record 1

Record 1

Rowid 10240


Details Part III

Make it real

Commit the updates

Release or downgrade locks


End Transaction

Transaction Table (-n)Usrctl (-n)

User Id 9Trans Id 2433405

Release Transaction Entry

Write Commit Note/do commit processing


SSSS EQEQ

Free List


HashTable

(-lkhash)

Release/Downgrade Locks

XX SQSQ SQSQ SQSQ

XX

SQSQ

Awaken users waiting on lock

Release exclusive lock

SQSQSQSQ EQEQSQSQXX SQSQ EQEQ


In Summary

YOU: Simple Update WE: Lots of work You can Enhance the

Process


Questions?


Thank you for your time!

db-08: a day in the life of a type ii record richard banville progress fellow

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