RE: shared pool evictions

From: Noveljic Nenad <>
Date: Tue, 3 Mar 2020 23:54:48 +0000
Message-ID: <>

Ø How many times did you execute that child cursor?

Ah, that’s the point. Only after the 3rd execution the cursor gets cached by the session. After that it doesn’t get evicted from the shared pool that easily. Consequently, I’ll try to extend the life expectancy in the shared pool by increasing session_cached_cursors. On a low-activity test database the SQL doesn’t get evicted for the long time even when the cursor isn’t cached by a session.

By the way, this list is attended by many smart people, and it trumps any payed support by far. Whenever I ask a (at least, for me) non-trivial question not only do I quickly get a solution, but I also learn a bunch of new stuff. I’m so grateful for all the advice I’ve received so far.

Best regards,


From: Tanel Poder <> Sent: Dienstag, 3. März 2020 22:24
To: Noveljic Nenad <> Cc:; ORACLE-L ( <> Subject: Re: shared pool evictions

How many times did you execute that child cursor?

If you execute it only once (pinned only twice), the cursor's recreatable chunk will stay in the transient part of the LRU list. If you execute it more times, but a new child gets created after the last exec, then the new child would have been executed only once and can age out quicker than previous multi-executed cursors.

I don't know of any X$ or dumps that would tell you whether a chunk is in transient or recurrent part of the LRU list, but you can see the current totals from X$KGHLU:

SQL> _at_kghlu

---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------- ---------- ---------- ---------- -----------
         1          0    4966364   15091924      14034      14898          0           0       8694          0          0           0

That's why when I do live demos that require the cursor to be around for a bit longer, I run my demo queries 2-3 times (executions 2 should be enough though).

Also, if your shared pool is split into multiple subpools, what happens to get aged out depends on whatever subpool some other shared pool allocator defaults to using.

Tanel Poder

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Received on Wed Mar 04 2020 - 00:54:48 CET

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