Picture Perfect 4.6 Enterprise Edition User Manual - UTCFS Global ...

100Picture Perfect 4.6 Enterprise EditionUser Manual7 Is native Informix replication used for all the tables?Native information replication is used for all tables listed above. The history tables continue to usethe database refreshers.8 Does ER need the modify date/time information to be maintained?The main purpose of modify date/time was for the refreshers to determine which record was morerecent and refresh accordingly. Informix ER has its own timestamp column and rules to determinethis. Even though we are continuing the maintenance of the modify date/time fields, there is no needfor this information anymore.9 How are conflicts handled when changes are made on two hosts at the same time?There are two cases when conflicts may arise:• Conflicts during normal ER operation are resolved with the timestamp rule: the last change"wins". See Table 9 for a more detailed explanation.Table 9.Conflict Resolution Based on the Time StampRow exists onthe target?Time StampDatabase OperationInsert Update DeleteNo n/a Apply row Apply row (ConvertUPDATE to INSERT)Yes T last_update< T replApply row (ConvertINSERT to UPDATE)T last_update> T replDiscard rowApply rowApply row (INSERT intoER delete table)Apply rowT last_update= T replApply row if no routine is defined as a secondary conflict resolution rule.Otherwise, invoke the routine.• Conflicts during a subhost recovery or using ercmd.sh are resolved with a "master" host.This means that if records are identical with the master, even though they have a greatertimestamp, the master record always wins.There are only 2 cases when this comes into play:- If changes are made on a subhost while an upgrade is in progress (that is, the subhostwas acting as a standalone), the changes will be lost.- If a subhost was removed from the ER configuration and changes were made locally, thechanges are lost when the subhost is added back into the ER.Note: Inserts will be preserved.10 What happens if the same table record (same primary key value) is updated from two hosts at the same time (same timestamp)?In this case, the host with the lower group id' wins. In our configuration, the nethost always has thelowest (group id=1) and the subhosts have ids in the order that they were added to the system.You can see the group id information in the /cas/db/etc/sqlhosts file.