![]() ![]() This would be expected with multiple, heavy-hitting applications working against the same PostgreSQL Instance. A general rule in PostgreSQL is that as the number of active, concurrent transactions ( pg_stat_activity.state = 'active') exceeds 2 times the number of CPUs, we begin to experience CPU load saturation. The next two sections illustrate CPU and Memory factors that come into play with PostgreSQL being a host to 2 or more heavy-hitting applications.Ī PostgreSQL instance that has multiple heavy-hitting, DML applications connected to it can have CPU load problems due to the fact that we are stacking up or accumulating the concurrent, active transactions of multiple applications. So, the "right" solution without some re-architecture and/or use of 3rd party tools and extensions is to migrate the applications off of Oracle RAC one at a time to separate PostgreSQL instances, one heavy-hitting application per PostgreSQL Instance. While Oracle RAC can divvy up the applications and load balance them across the Nodes in the cluster, there is no such thing in PostgreSQL. The big picture that is missed here is ACTIVE-ACTIVE (Oracle RAC) and ACTIVE-PASSIVE (PG). ![]() A common mistake with migrations from Oracle RAC farms is to associate all of the farm applications with one PostgreSQL Instance. With RAC you may have multiple, separate, heavy-hitting, DML applications usually of the OLTP type connected to the same RAC Cluster, where RAC serves as a type of application farm. Oracle Enterprise has a more direct migration to PostgreSQL than does Oracle Real Application Clusters (RAC) in some cases. Postgres 8.4, and sometimes this also works for earlier versions.Oracle 12c is in some aspects different (Multitenent DB) but migration may be even easier.Oracle 10g to 11g (most stuff will work down to 8i).If you're porting Oracle SQL to Postgres SQL for theĪCS/pg, you should also be quite familiar with AOLserver Tcl, especially the AOLserver database APIs. Knowing the details of Oracle SQL and Postgres SQL are obviously tremendous advantages, but the hints in this document should quickly bring you up to speed on what the differences are. 2 Oracle Enterprise and RAC Considerations.1 What you should know before you begin.‘None of the above’ is our default value, in case our expression is not equal to any search value. ![]() The DECODE function compares our expression with all the search values and returns the result corresponding to that search value. In this query, our expression is 1 + 1 and 1, 2, 3 are search values while ‘One’, ‘Two’, ‘Three’ are results corresponding to each search value. Lets understand how a DUAL function works with the help of a simple example: Examples 1.DECODE Function with DUAL Table If default value is omitted from the query, the DECODE function returns NULL. If expression does not match any of the search value, then the query returns the default value. The data type of the returned value is the data type of the first result value that is returned. If we don’t provide default value then query returns NULL. If expression is equal to search1 is returned, if it equal to search2 then result2 is returned and so on.ĭefault – If expression is not equal to any search value, then the query returns the default value. Result – If expression value is equal to the search value, then the DECODE function returns result. The data types of all subsequent search values are converted to the data type of first search value. Search – These are the values against which expression is compared. The data type of this value is converted to the data type of the first search value before comparing. Expression – This is the value that we provide to compare with other search values.
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