Unique Columns For V$Sql


Until yesterday I was saying SQL_ID and CHILD_NUMBER is enough to get a sql child cursor from V$SQL and today I know I was wrong.

Probably many times you needed the sql statement that a session is running. To do that you query V$session and find the session information and then use SQL_ID column to reach out V$Sql. if you write a query like this:

you can write any filter you want here but you will immediately realized that some session rows are multiplied. Why? Because you didn’t use “CHILD_NUMBER” while reaching v$sql. V$SQL is not main data source for unique sql statements in your database. V$SQLAREA is. So instead of v$sql, you can use v$sqlarea in this query but if you need specific information about the exact sql cursor that session is currently running then you must use v$sql.

Note: I will not go deep Parent-Child cursors here. basically, every sql statements has child cursors. they all same sql but for some reason they have different properties and your session is running a “child cursor”.

so your query should be like this:

and now you reached to exact correct sql child cursor that is running for that session. right? well, I did know so but I find out, it is not! On one of my clients system, I discovered that this query returns 2 rows from v$sql which means for same SQL_ID and CHILD_NUMBER there are 2 rows in v$sql. I couldn’t find anything on docs or google (maybe couldn’t search enough) and started to dig about this sql statements.

here is the necessary information about this sql:

almost everything is same but ADDRESS and CHILD_ADDRESS. CHILD_ADDRESS is the memory address that this cursor resides on so it must be different obviously. Only thing that create this difference is ADDRESS column. ADDRESS column in V$sql is the address of the PARENT cursor which is in V$SQLAREA view. So let’s check this view:

there is only one of them exists. So some of those child cursors in v$sql are not (I am not sure the term) “valid”. they might be used before (and they were in my example) but now they are remaining of a past sql. So which child cursor in v$sql is the sql statements that session is currently running? Now we need to use ADDRESS column too. SQL_ADDRESS column in v$session is the parent address of the sql statement. So, I should add it into my queries too:

thanks for reading. comments are welcome. wish you healthy happy days.

Leave a Reply

Your email address will not be published. Required fields are marked *