ODBC Driver for Teradata determines if a DNS contains cop entries for the database name. The first attempt to resolve the database name has a cop1 suffix appended. Cop discovery is disabled if a cop1 entry is not defined in DNS. All resolutions will be made for this name without adding the cop suffix, and no further attempts to resolve cop1 will be attempted.
If an entry for cop1 is found in DNS, then it is assumed that DNS contains further cop entries for the database name. However, the number of entries is not known. Subsequent resolutions will increment to the next number and attempt to find an entry in DNS. The first entry that is not found in DNS marks the last entry for the given name. At that point the list of DNS entries is complete. The first connection attempt chooses a random number between the first and last cops found. Each subsequent connection will increment to the next number (round-robin).
If multiple database names are provided in ODBC DSN, and the first name has no cops defined, all names will be resolved without adding a cop suffix. No attempt will be made to find the number of cops defined.
In order for ODBC Driver for Teradata to discover the last entry in the sequence, a DNS resolution must fail. DNS resolutions which result in a failure might be time consuming, depending on how the DNS is configured. If a name lookup failure in the DNS is time consuming, type the number of DNS-defined cops into the Datasource DNS Entries field. If additional entries are added to DNS at a later time, they will be discovered by ODBC Driver for Teradata (if Data Source DNS Entries is not set or undefined).
For more information about how to modify cop handling, see Data Source DNS Entries in Teradata ODBC Driver Advanced Options.