IBM Haifa Research Laboratoryresearch.ibm.com/haifa/Workshops/SystemsAndStorage...© 2002 IBM...

© 2002 IBM Corporation

IBM Haifa Research Laboratory

IBM Systems and Storage Seminar | 24/11/2003

Improving Database Functionality and Performance Using an Object Store Architecture

Gary Valentin Noam Rinetzky Michael Factor


Improving Database Functionality and Performance Using an Object Store Architecture © 2002 IBM Corporation2

Research Goals

§Potential benefits of Object Stores (ObS) to Data Base Managers (DBM)

§Effects of ObS technology on DBM design

§Making ObS more attractive for DBM√

√

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Outline

§Background– Database managers storage model

– Object Store

§DBM / ObS§Expected benefits§Prototype Implementation §Related work§Conclusions



Database Managers

Programs that manage data§ Insert, delete, update, query, etc. via SQL§Advanced services

– Backup, transactional access, …

§Responsible for storing the data– Store data in tables and indexes

– Use various data structures

– B+Trees, heaps, …– Data layout is invisible to end-user



DBM Storage ModelsFile system

managed data§ DBM: places each table

and index in a separate file§ File system: manages

the storage

DBM managed data

§ DBM works with raw partitions§ Takes responsibility

for storage management

ObSmanaged data

DBM

Block Device

DBM

Object Store

DBM

Block Device

File System



What is an Object Store?

What is a block device?§ Abstraction: array of unrelated

blocks§ Access: based on block

number

What is an object store?§ Abstraction: collection of

storage objects§ Access: object id, range

0x1000x000

0x3000x200

0x4000x400

…

O2 O4

O1O3

O5



What is an Object Store?

ObS interface§ Create / delete object§ Read / write byte range in an

object§ Set / Get object attributes

O2 O4

O1O3

O5

ObS is responsible for§ Managing object meta data

– Offset à data

– Attributes§ Free space management

ObS provides a higher level of abstraction

What is an object store?§ Abstraction: collection of

storage objects§ Access: object id, range



DBM ObS Storage Model

§ Each table / index is mapped to a different storage object§ By design, similar to the

FS-MD modelHowever, storage management is done by the ObS and not by the file system



Expected Benefits

Performance§Code path

reduction § Improved caching §Atomic writes§Advanced Search

Functions

Functionality§Quality of Service §Object point in time

copy§Object encryption§Object compression



Performance Boosting via Code Path Reduction§ ObS-MD minimizes the

storage management code path on the DBM host

FS-MD: FS-layer overhead

DBM-MD: DBM Storage management overhead

ObS-MD: Storage management overhead moved to storage server

§ Conjecture: moving work from DBM host to the storage server is beneficial



Object Compression

Pros§ Transparent to DBM§ Does not use DBM host

CPU cycles§ Efficient compression

– large blocks

Cons§ Complicates object

updates§ Does not save network

bandwidth

ObS can provide lossless object compression

The DBM may choose to compress only suitable objects

e.g. rarely modified large text objects



Prototype Implementation

§Modified DB2 Universal database V8.1 to use a native ObS interface§Changed components

– Data cache

– Agents

– Prefetchers

– Page cleaners

§ Internal object store prototype



Object Caching

§ Prototyped the ability to specify which objects to cache§ Scanned tables:

– 60MB size

– 1M records

Conclusions• Performance gained by caching object in the ObS cache approaches optimal• Changing the ObS caching policies, i.e., according to QoS considerations can influence the DBM overall performance



Related Work

§Object Stores:NASD [G. Gibson et al., 1997]

ObS Security [Gobioff 1999, A. Azagury et al., 2002]

T10 OSD standard §DBM & Storage

My cache or yours? [T. M. Wong and J. Wilkes 2002]

Lachesis [B. Schindler et al. 2003]

Active storage [E. Reidel et al. 1998]



Conclusions

Object store managed data model

§ An attractive alternative to current storage models§ Provides many benefits

– Performance: code path reduction, caching, advanced search function, atomic writes

– Functional: QoS, point in time copy, object encryption, object compression

§ Benefits originate from – ObS higher level of abstraction

– DBM deep understanding of the objects it maintains

§ Fits well with current DBM design



?



Advanced Search Functions

§A search of a string in a not-indexed column leads the DBM to read an entire table§An advanced search function would allow

the DB to send the string to the OBS and get back the offsets in an object in which a match was found§Save network bandwidth and CPU cycles

from DBM host



Atomic Writes

§ SCSI Block devices guarantee atomic writes at sector granularity§ DBM manages tables with

different page sizes– e.g., 4K, 8K, 16K, 32K

§ Pages has to be written atomically§ Partial page is an unrecoverable

situation

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4K page = 8 sectors

Can dofrom log

Can undo from log

ObS solution: set atomic write length as an object property

Restore from backup

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