It is easier to create one or two AWR reports quickly using OEM. But, what if you have to create AWR reports for many snapshots? For example, your Oracle support analyst wants you to supply 10 1-hour AWR reports from 10AM to 8PM in a 8 node cluster? That’s about 80 AWR reports to create! Okay, okay, I may(!) be overselling it, but you get the point. It is useful to have a script to create AWR report for all instances for a given range of snapshot IDs. Following scripts are handy:
I will be hacking RAC internals with few LINUX tools in Oaktable world presentation series, in SFO. Details are available at Oaktable World 2013
Hope to see you there!
I blogged about DFS lock handle contention in an earlier blog entry. SV resources in Global Resource Directory (GRD) is used to maintain the cached sequence values. I will further probe the internal mechanics involved in the cached sequences. I will also discuss minor changes in the resource names to support pluggable databases (version 12c).
Let’s create an ordered sequence in rs schema and then query values from the sequence few times.
create sequence rs.test_seq order cache 100; select rs.test_seq.nextval from dual; -- repeated a few times. ... / 21
Sequence values are permanently stored in the seq$ dictionary table. Cached sequence values are maintained in SV resources in GRD and SV resource names follows the naming convention to include object_id of the sequence. I will generate a string using a small helper script and we will use that resource name to search in the GRD.
A quick note, Expert Oracle RAC book co-written by me is available now: Expert Oracle RAC 12c. I have written about 6 chapters covering the RAC internals that you may want to learn I even managed to discuss the network internals in deep, after all, network is one of the most important component of a RAC cluster.
This blog entry is to discuss a method to identify the objects inducing higher amount of redo. First,we will establish that redo size increased sharply and then identify the objects generating more redo. Unfortunately, redo size is not tracked at a segment level. However, you can make an educated guess using ‘db block changes’ statistics. But, you must use logminer utility to identify the objects generating more redo scientifically.
Detecting redo size increase
AWR tables (require Diagnostics license) can be accessed to identify the redo size increase. Following query spools the daily rate of redo size. You can easily open the output file redosize.lst in an Excel spreadsheet and graph the data to visualize the redo size change. Use pipe symbol as the delimiter while opening the file in excel spreadsheet.
The restart of a UNIX server call initialization scripts to start processes and daemons. Every platform has a unique directory structure and follows a method to implement server startup sequence. In Linux platform (prior to Linux 6), initialization scripts are started by calling scripts in the /etc/rcX.d directories, where X denotes the run level of the UNIX server. Typically, Clusterware is started at run level 3. For example, ohasd daemon started by /etc/rc3.d/S96ohasd file by supplying start as an argument. File S96ohasd is linked to /etc/init.d/ohasd.
S96ohasd -> /etc/init.d/ohasd /etc/rc3.d/S96ohasd start # init daemon starting ohasd.
Similarly, a server shutdown will call scripts in rcX.d directories, for example, ohasd is shut down by calling K15ohasd script:
Just a quick note, I will be presenting on “Truss, pstack, pmap, and more” talking about advanced UNIX utilities and how it can be utilized to understand inner working of an application or even Oracle Database Engine.
My timeslot is between 2:15 and 3:15 in Room 2016.
Uploading presentation files. Thanks for attending at OOW12.
This is a quick note about reverse path filtering and impact of that feature to RAC. I encountered an interesting problem recently with a client and it is worth blogging about it, with a strong hope that it might help one of you in the future.
Environment is 126.96.36.199 GI, Linux 5.6. In a 3 node cluster, Grid Infrastructure (GI) comes up cleanly in just one node, but never comes up in other nodes. If we shutdown GI in first node, we can start the GI in second node with no issues. Meaning, GI can be up in just one node at any time.
System Admins indicated that there are no major changes, only few bug fixes. Seemingly, problem started after those bug fixes. But there were few other changes to the environment /init.ora parameter change etc. So, the problem was not immediately attributable to just OS changes.
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).
We know that database blocks are transferred between the nodes through the interconnect, aka cache fusion traffic. Common misconception is that packet transfer size is always database block size for block transfer (Of course, messages are smaller in size). That’s not entirely true. There is an optimization in the cache fusion code to reduce the packet size (and so reduces the bits transferred over the private network). Don’t confuse this note with Jumbo frames and MTU size, this note is independent of MTU setting.