Let’s first discuss how RAC traffic works before continuing. Environment for the discussion is: 2 node cluster with 8K database block size, UDP protocol is used for cache fusion. (BTW, UDP and RDS protocols are supported in UNIX platform; whereas Windows uses TCP protocol).
UDP protocol, fragmentation, and assembly
UDP Protocol is an higher level protocol stack, and it is implemented over IP Protocol ( UDP/IP). Cache Fusion uses UDP protocol to send packets over the wire (Exadata uses RDS protocol though).
The basic formula for calculating the costs of a Nested Loop Join is pretty straightforward and has been described and published several times.
In principle it is the cost of acquiring the driving row source plus the cost of acquiring the inner row source of the Nested Loop as many times as the driving row source dictates via the cardinality of the driving row source.
Cost (outer rowsource) + Cost (inner rowsource) * Card (outer rowsource)
Obviously there are cases where Oracle has introduced refinements to the above formula where this is no longer true. Here is one of these cases that is probably not uncommon.
May 20, 2012 An interesting quirk was recently brought to my attention by Mich Talebzadeh. He generated a 10046 trace at level 8 for a session, executed some SQL statements, disabled the trace, and then processed the resulting trace file with TKPROF. His TKPROF output included the following: UPDATE TESTWRITES SET PADDING1 = RPAD('y',4000,'y') WHERE [...]
The last of Jack’s relatives are gone. Are his girlfriend (Gia), her daughter (Vicky) and Jack’s unborn child the next in line? Is there anything Jack can do to protect them?
This book focuses more on Jack’s relationship to “The Otherness” and “The Ally”. We see a more aggressive side of Jack, as well as the cold calm detachment when he’s doing his job. Dark, dark, dark, but also kinda exciting.
I've built up quite a list of upcoming events that I want to blog about, so I'll deal with them in a single post (... then the OUGN review and then *finally*, *maybe* a technical post or three ...)
Chris Date Seminar
It amazes and amuses me how many times I remember something that I used to know but forgot due to lack of use. I'm not sure if it's because I'm just getting older or what. :)
I had just created a SQL Profile and set the force_matching option to yes so that any SQL that had the same signature would be covered by this profile. If you need a reminder, what the force matching signature does is to treat literals in the SQL like binds (think along the lines of cursor_sharing = force). When force matching is in place, all the literals are treated as binds and the same signature is generated for any SQL that differs only by their literals (white space and case are handled already).
I was in a discussion recently about how to estimate the size of a bitmap index before you build it, and why it’s much harder to do this for bitmap indexes than it is for B-tree indexes. Here’s what I wrote in “Practical Oracle 8i”:
An interesting feature of bitmap indexes is that it is rather hard to predict how large the index segment will be. The size of a b-tree index is based very closely on the number of rows and the typical size of the entries in the index column. The size of a bitmap index is dictated by a fairly small number of bit-strings which may have been compressed to some degree depending upon the number of consecutive 1’s and 0’s. To pick an extreme example, imagine a table of one million rows that has one column that may contain one of eight values ‘A’ to ‘H’ say, which has been generated in one of of the two following extreme patterns:
I just checked to find out that there has been 3,000 downloads of SLOB – The Silly Little Benchmark. People seem to be putting it to good use. That’s good.
Before I get very far in this post I’d like to take us back in time–back before the smashing popularity of the Orion I/O testing tool.
When Orion first appeared on the scene there was a general reluctance to adopt it. I suspect some of the reluctance stemmed from the fact that folks had built up their reliance on other tools like bonnie, LMbench, vxbench and other such generic I/O generators. Back in the 2006 (or so) time frame I routinely pointed out that no tool other than Orion used the VOS layer Oracle I/O routines and libraries. It’s important to test as much of the real thing as possible.
If you’ve known me for a long time, and let’s face it, if you’re visiting this blog, you probably do, you know that I’m particularly proud of the work I was able to do at Network Solutions as the Director of Database Engineering and Development.