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HP NonStop Shadowbase Command Definitions

Database Specification Command Descriptions

HP NonStop Shadowbase Command Reference Manual—785421-002

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source and the target databases would continue to diverge (not

synchronize).

 In this new version of HP Shadowbase, the original duplicate key error

on the INSERT of the row with primary key value of 2 and a unique

index value of 1 would be identified as a collision on the unique index,

and with the a new DBS parameter enabled (DELUIDXDUP), the

target row that caused the collision (the fellow with a primary key value

of 1 and a unique index value of 1) would be deleted, and the INSERT

of the incoming row with a primary key value of 2 and a unique index

value of 1 would be re-applied successfully. This causes the target

database to converge to the source database’s values (synchronize).

A similar (abbreviated in the example below) sequence occurs in the

previous versions of HP Shadowbase for an active-active bi-directional

replication scenario with one application running on each node as follows:

 Assume application #1 is running on node 1 against its local database,

and inserts a row into its table A with primary key = 1 and unique index

= 1.

 At the same instant, assume application #2 is running on node 2

against its local database, and inserts a row into its own table A with

primary key = 2 and unique index = 1.

 Each of these inserts will locally succeed, but when they are replicated

to the other node they will fail with a duplicate key error on the unique

index. At this point, the tables will be left out-of-sync with table A on

node 1 containing one row with (1,1) in it, and table A on node 2

containing one row with (2,1) in it.

Using the new HP Shadowbase collision resolution parameter

(DELUIDXDUP), HP Shadowbase will stubbornly, forcefully apply an

incoming I/O and when the duplicate key error occurs on the index, it will

locate the offending target row with the offending unique index value and

remove it, allowing the incoming I/O to be successfully applied. In other

words, the target is made to look like the source.

In a bi-directional example, you would generally only enable this new

parameter (DELUIDXDUP) in one direction, and probably enable the key-

replay (KREP) feature of HP Shadowbase (also refer to the HP

Shadowbase High Availability Designated Winner (SBHADW)

documentation as that, by default, enables DELUIDXDUP for Master ->

Slave links, and disables DELUIDXDUP for Slave -> Master links).

DOIFNOAUDATSTART {CONTINUE}

{STOP}

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