Transcript Materialized Views: Simple Replication? - Go

Materialized Views:
Simple Replication?
David Kurtz
Go-Faster Consultancy Ltd.
[email protected]
www.go-faster.co.uk
UKOUG DBMS SIG 17.7.07
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Who Am I?
• Oracle Database Specialist
– Independent consultant
• System Performance
tuning
• Book
– www.psftdba.com
– PeopleSoft ERP
– Oracle RDBMS
• UK Oracle User Group
– PeopleSoft Director
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Agenda
• Simple Replication using Materialized
Views
– Database Links
– Limitations
• Aspects of the application (PeopleSoft)
• Workarounds
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Resources
• If you can’t hear me say so now.
• Please feel free to ask questions as we go
along.
• The presentation will be available from
– www.ukoug.org in the library
– www.go-faster.co.uk
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Initial Scenario
HRMS
Assentia
l Data
Stage
CRM
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EPM
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Initial Scenario
• Extract from HR and CRM to EPM
– Via Assential Data Stage
• Table by Table replication by SQL
• Capability to transform data
• Limited Capability to handle long columns
– Performance Bottleneck
• Taking too much of batch window which was
needed for other batch processing
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Materialized Views – v- Streams
• Materialized Views
– Used to be called
snapshots
– Old stable technology
– Database links between
databases
– Also used for query
rewrite
• Streams
– Introduced 9i
– Supplemental logging
shipped to target
database.
– No support for Longs
in Oracle 9i
• Not discussed in this
presentation
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• PeopleTools 8.45
• Lots of LONG columns
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The Plan
• Eliminate Assential (as far as possible)
– Some complex transitions remain
– Implement incremental refresh for all MVs
• Incremental refresh every midnight
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Problem 1: Long Columns
• Long Columns
– Assential works in blocks of 2000 characters
• We discovered truncated data in long columns
– Replicate up to 32Kb with MVs
• workaround to go across DB links.
– Oracle 10g Streams would provide a total
solution.
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Problem 2:Primary Keys
• PeopleSoft doesn’t use database enforced
Referential Integrity
– No primary keys, only unique constraints
• Can usually add primary key constraints using
existing unique indexes
– Can get Nullable date columns in unique key
• Can’t add a primary key constraint
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MVs
MV
Refresh
Source
Table
MVL
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Target
MV
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MV Replication Choice
• No Primary Key
• Primary Key
– ROWID based
replication
– No inherited indexes or
keys
– You may need to create
unique indexes on MV
– What happens if you
reorganise the table?
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– Replication by primary
key
– MVs and MV logs
inherit primary keys
– Effect of Truncate
command?
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Effect of TRUNCATE
• Primary Key
replication
• ROWID replication
– Rows not removed
from MV by fast
refresh
– No error raised
– Need to do complete
refresh
– ORA-12034 during
fast refresh
– materialized view log
on <table> younger
than last refresh
– Need to do complete
refresh.
• Demo mv1.sql
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• Demo mv2.sql
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MVs with Long Columns
MV
Refresh
Source
Table
MVL
Trigger
Target
MV
Long
Table
View
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MVs with Long Columns
• This solution would occasionally lock up
– Distributed Xaction Lock
• Visible in DBA_WAITERS
–
–
–
–
Unrelated statements
Every 2 or 3 weeks
Never reproduced outside production system
Kill a session created by the MV refresh
process
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Distributed Transaction Lock
• MV Refresh Process
• Long Query in Trigger
SELECT /*+ */
"A2"."APPLID", "A2"."APP_DT",
"A2"."APPLIC_PURGE_DT", ...
"A2".“XX_PRIOR_RECR",
"A2"."JOB_CAT",
"A2".“XX_GRAD_OR_STANDRD"
FROM "SYSADM"."PS_APPLICANT_DATA"
"A2",
(SELECT /*+ */ DISTINCT "A3"."APPLID"
"APPLID", "A3"."APP_DT" "APP_DT“
FROM
"SYSADM"."MLOG$_PS_APPLICANT_D
ATA" "A3"
WHERE "A3"."SNAPTIME$$" > :1
AND "A3"."DMLTYPE$$" <> :"SYS_B_0")
"A1"
WHERE "A2"."APPLID" = "A1"."APPLID"
AND "A2"."APP_DT" = "A1"."APP_DT"
SELECT "A1"."COMMENTS"
FROM "SYSADM"."PS_ABS_HIST_DET"
"A1"
WHERE "A1"."EMPLID" = :b5
AND "A1"."EMPL_RCD" = :b4
AND "A1"."BEGIN_DT" = :b3
AND "A1"."ABSENCE_TYPE" = :b2
AND "A1"."COMMENT_DT" = :b1
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Distributed Transaction Lock
• When Oracle performs a distributed SQL
statement it reserves an entry in the rollback
segment for the 2-phase commit processing. The
entry is held until the statement is committed, even
if the statement is a query.
www.jlcomp.demon.co.uk/faq/dblink_commit.sql
• The commit in the MV refresh does not release it
– So we put query of long into autonomous transaction in
a PL/SQL packaged function
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Irony
• We never tested the fix to the locking
problem
– Interim workaround was simply not to replicate
long columns
• Disabled trigger on MV
– Change in customer personnel removed need to
replicate long columns
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More Irony
• Can replace LONGs with BLOBs and
CLOBs in PeopleTools 8.48
– Default in HR and Financials 9.0
– Most people moving to this release on Oracle
RDBMS are also moving to Oracle 10g
– In Oracle 10g, I would probably have chosen to
implement Streams.
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Questions?
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