Does TAF SELECT failover work with any type of database configuration (replication, standby, cold failover), or is OPS required?
TAF SELECT failover is supported with any type of database, OPS is not required. A cluster failover (Fail Safe, ServiceGuard, FirstWatch, etc) would work just as well–it’s the same database, just running on a different node. Also, SELECT failover will work with a replicated or standby database. However, because these databases are not identical to the primary database (a standby may be a few logs behind and a replicated database can have other records), the likelihood that the first n rows returned by the restarted query not corresponding to the n rows returned before the failure increases. Oracle (OCI library) detects this by calculating a checksum on those first n rows and comparing it to the running checksum it was calculating before the failure. If they are the same, Oracle assumes the first n rows are identical and discards those rows because they have already been returned. If they are not identical, Oracle returns an error message.
TAF SELECT failover is supported with any type of database, Real Application Clusters or OPS is not required. A cluster failover (Fail Safe, ServiceGuard, FirstWatch, etc) would work just as well–it’s the same database, just running on a different node. Also, SELECT failover will work with a replicated or standby database. However, because these databases are not identical to the primary database (a standby may be a few logs behind and a replicated database can have other records), the likelihood that the first n rows returned by the restarted query not corresponding to the n rows returned before the failure increases. Oracle (OCI library) detects this by calculating a checksum on those first n rows and comparing it to the running checksum it was calculating before the failure. If they are the same, Oracle assumes the first n rows are identical and discards those rows because they have already been returned. If they are not identical, Oracle returns an error message.
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