April 22, 2012 (Modified April 24, 2012)
I had intended to finish assembling the second half of the “Oracle Database 11gR2 Performance Tuning Cookbook” book review, however my free time that may be dedicated to book reviews has been a bit limited lately (I have a review of another book started, but left untouched for the last three months). On a side note, I am a little shocked that none of the 21 errata reports that I filed for the first 88 pages of the book made it onto the publisher’s website, but maybe that is not too uncommon (the same has happened for at least one Apress book).
I encountered an interesting quote on page 252 of the “Oracle Database 11gR2 Performance Tuning Cookbook” that I thought I would share with readers:
“The PCTINCREASE parameter cannot be specified when we use the AUTOALLOCATE option for the tablespace. We can have different tablespaces for each database user and we can query the dynamic performance view V$SORT_USAGE to retrieve the details about the active disk sorts occurring in the instance.
We can obtain better performance by striping the temporary tablespace using multiple disks. Please note that – due to their nature – temporary tablespaces are not affected by backup and restore operations.”
If you own the book, start on page 251 and read through the end of page 252. – there are a couple of additional interesting sentences in this section of the book
What, if anything, is wrong with the above quote from the book? For those readers that need some assistance with this task, the Oracle Database 11.2 documentation might be helpful.
The point of blog articles like this one is not to insult authors who have spent thousands of hours carefully constructing an accurate and helpful book, but instead to suggest that readers investigate when something stated does not exactly match what one believes to be true. It could be that the author “took a long walk down a short pier”, or that the author is revealing accurate information which simply cannot be found through other resources (and may in the process be directly contradicting information sources you have used in the past). If you do not investigate in such cases, you may lose an important opportunity to learn something that could prove to be extremely valuable.
(Added April 24, 2012, my book review notes for the four quoted sentences, plus one of the preceding sentences)
- The book’s discussion of defining the INITIAL and NEXT storage parameters for temporary tablespaces as a multiple of the SORT_AREA_SIZE parameter seems to be out of place in an Oracle Database 11g R2 performance tuning book – dictionary managed tablespaces were deprecated with the release of Oracle Database 9.2, and the effect of these parameters is different in locally managed tablespaces (page 252).
- The book states, “The PCTINCREASE parameter cannot be specified when we use the AUTOALLOCATE option for the tablespace.” This statement appears to be incorrect – the Oracle Database documentation states that a specified value for PCTINCREASE will be ignored when creating an AUTOALLOCATE tablespace (page 252).
- The book states, “We can have different tablespaces for each user and we can query the dynamic performance view V$SORT_USAGE to retrieve the details about the active disk sorts occurring in the instance.” This statement is a bit confusing, so it is probably best to break the sentence into two separate logical sentences for analysis. The first half of the statement seems to suggest that a separate temp tablespace should (or could) be created for each user – I am not sure that this is the author’s intended interpretation; the default temporary tablespace may be set at the user level so that not all users are required to use the same (default) temporary tablespace. For the second logical sentence, the V$SORT_USAGE performance view was deprecated with the release of Oracle Database 9.2, replaced with V$TEMPSEG_USAGE. In Oracle Database 11.2 (the version mentioned on the book’s front cover), the V$SORT_USAGE view is based on the GV$SORT_USAGE view which selects from X$KTSSO (confirm by issuing SELECT VIEW_DEFINITION FROM V$FIXED_VIEW_DEFINITION WHERE VIEW_NAME=’GV$SORT_USAGE’;). The GV$SORT_USAGE view definition, which is pointed to by both the V$SORT_USAGE and V$TEMPSEG_USAGE synonyms, indicates that the SEGTYPE column values may be one of SORT, HASH, DATA, INDEX, LOB_ DATA, LOB_INDEX , or UNDEFINED. The potential values of the SEGTYPE column suggests that the view potentially shows a variety of activity in addition to what the book mentions (the WHERE clause should be adapted to restrict the rows returned from this view, so that the results are consistent with this chapter’s contents). The V$SORT_USAGE view also shows entries for aborted SQL statements, for instance when Ctrl-C is pressed in SQL*Plus and another SQL statement has not been executed by the session (page 252).
- The book states, “Please note that – due to their nature – temporary tablespaces are not affected by backup and restore operations.” This is a vague statement at best, and the accuracy of the statement depends in part on the type of backup performed (online or offline, user-managed or RMAN hot backup, etc.). An online RMAN backup will not back up the tempfiles of locally managed temporary tablespaces; however, when those backed up databases are restored and recovered, Oracle Database 10.2 and later will recreate the temporary tablespace tempfiles when the database is opened (page 252).