An example of EXPLAIN output on DB2 ESE Solaris is shown below:
SQL Statement: select acct_type from dntnck.account_xref Estimated Cost = 3 Estimated Cardinality = 1000 Distributed Subquery #1 #Columns = 1 Return Data to Application #Columns = 1 Distributed Subquery #1: Server: HOST390 (DB2/390 7.1) Subquery SQL Statement: SELECT A0."ACCT_TYPE" FROM "TST1TXP"."ACCOUNT_XREF" A0 Nicknames Referenced: DNTNCK.ACCOUNT_XREF ID = 165 Base = TST1TXP.ACCOUNT_XREF
The output shows the Federated Database translation of the nickname into the target table residing on the OS/390. To see the access path from the HOST390 server, you must use the Visual Explain for the OS/390.
A few differences between the Visual Explain implemented on UNIX (i.e., Solaris) and on OS/390 are listed below.
Under the current federated database system, both UNIX and OS/390 EXPLAIN will be required to get a complete picture of query performance. On UNIX, we will expect to see a very simple plan consisting ideally of a fetch from a remote query. To see which indexes and join paths, etc., are used, we will need to look at the DB2 for OS/390 EXPLAIN.