Installing D6 on Oracle RAC

June 12, 2008 at 5:13 pm | Posted in D6, Documentum and Oracle, Performance | 1 Comment
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It’s a tricky business keeping Release Notes up-to-date. I’ve just been browsing through the latest D6 SP1 Release Notes and my attention was caught by a small section about installing on Oracle RAC:

Installing with Oracle Real Application Clusters (121442)
If you are installing Content Server with Oracle Real Application Clusters (RAC), set
the value of the Oracle parameter MAX_COMMIT_PROPAGATION_DELAY to 0 (zero).
This value is required to ensure that the data that Content Server uses is consistent across
all Oracle nodes. Values other than zero are not supported.

I presume this has been in the various Content Server release notes for a while and it would have been important as using the default (or any other value here) uses a commit scheme that can delay other Oracle nodes from seeing changes. Since a single Content Server session often uses more than one database session (if you use DF_EXEC_QUERY in a DFC query call you are asking Content Server to start a new Oracle session) and those sessions could be attached to 2 different Oracle RAC nodes the delay in seeing recently changed values could cause havoc.

Now I know what your thinking, since we would obviously prefer to have data available immediately why would Oracle not use 0 as the default and why wouldn’t everyone just set it to 0 anyway? The answer of course is that there is a cost to be paid in performance; having to issue network calls to propagate information about a commit could be very costly (certain platforms seemed to have real problems with it), so in many cases the the default setting was fine provided your Oracle application didn’t have functional problems.

However since Oracle 10g Release 2 this parameter is deprecated – Oracle now uses the ‘broadcast on commit’ behaviour implied by MAX_COMMIT_PROPAGATION_DELAY=0 automatically. The best overview of this change is given in this paper by Dan Norris. Since the Content Server in D6 is only certified for Oracle on 10g Release 2 the entry shown above in the Release Notes is no longer needed. In fact it you could argue it is positively harmful. As they say, forewarned is forearmed.

By the way I stumbled on this bit of information whilst perusing the ‘Support by Product’ section on Powerlink. It is currently under beta and contains amongst other things a section for Documentum Content Server. It’s basically a portal type view of Content Server support information, bringing together support notes, whitepapers, documentation (there’s a very nice Top manuals section) and so on. I think it’s a brilliant idea and I urge everyone to have a look and provide feedback to the support team.

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