UKOUG 2008 – Thursday

Too many late nights in the pub meant I started off the day feeling a bit rough, and I managed to pay £15.75 for a bowl of museli. Hotel breakfasts really have an enormous markup.

CERN – Luca Canali & Dawid Wojcik

Good slide on why they use ASM, in particular they are using it to hook up multiple RAID arrays and use ASM to mirror and stripe across them.

stripe alignment

Luca stress tested ASM using a 14 node RAC cluster connected to 26 storage arrays with 16 SATA drives per array.

seeing IOPS per drive of 100 and this scales all the way to 40K IOPS with 410 drives.

WOW. CERN have 550TB of storage.

LUCA seeing that a rebalance operation moves more data than you would initially think it would: excessive re-partnering.

Not using ASMLib but use device mapper instead.

partition disks to ensure only outer/faster part of the disk is used for storing data.

Some scripts that give them devid, device name, multipath name, & status.

RMAN Optimizations- Stephan Haisley

unused block compression

now using locally managed tablespace bitmap. if extent is not allocated. Gah only works to tape with oracle secure backup  – that is a marketing decision not technical. Does go to disk

Does not work when you have a restore point set!?!

Undo Optimization

in 11gR1 undo blocks that are part of committed transactions are not backed up. reduces the number of blocks in the backup, uses SCN numbers. Again only to tape with Secure backup. Though will work to disk

Backup Compression

10gR1 using bzip2 great (~70%) compression but slow. 11gR1 added ZLIB compression.

To use ZLIB you need advanced compression option

Multisection Backups

11gR1 split large datafile into smaller contiguous blocks or sections created in parallel. if backup fails it can restart from the failed section.

When doing block media recovery the recovery will only use the section required rather than have to read a full huge backup of a datafile.

Good demo of Data Recovery Advisor, which Stephan had a hand in creating.

Virtual Reality?: Can Oracle VM deliver the virtual RAC Grid – Steve Shaw

I really quite liked this presentations and I did learn a lot. Virtualisation in some ways is like an oncoming train and I suspect for some people it may be get aboard it or get ran over by it.

In fact, in some ways Steve’s style of presenting is a bit like a bullet train he really barely stops but he packed a lot of good stuff into his presentation.

RAC is supported on Oracle VM with 32-bit linux
there is a choice between HVM (Hardware virtualisation) and PV (paravirtualized)

PV means the guest O/S has to be modified.

Hardware virtualisation built into the chip

talking about live migrations (to a different server) of RAC hosts using Oracle VM – not yet possible, but one day?

performance of paravirtualisation better than HVM. However Intel VT-d seems to make a huge difference to performance, graph showing perf almost as good as native.

Inside ASM – Julian Dyke

Julian’s presentation concentrated on how extents (including the metadata) is placed on disk in normal and high redundancy and what happens to them when you perform various rebalancing tasks.

Variance as a Tool – Robyn Sands

Robyn has such a great way of presenting she appears very calm and in control while on stage and has such a mellifluous voice that you could listen for longer than 45 minutes.

Robyn comes from a process engineering background, and I think the main idea was to check for processes/sql that have wild variations in response time and try to understand why this is happening as these tend to be the problematic sql statements – though some variation could be due to cyclical events.

Optimising by throwaway – Daniel Fink

I think there is a lot to this technique – find where in an explain that lots of rows are being processed and then later on in someway being filtered out and tune this part so that you do less of the work that is getting thrown away.

This idea makes good logical sense I think. Dan is obviously a highly accomplished speaker but it was a real shame he got the timing badly muddled up and spent really far too long explain the (pretty simple concept) and then had practically no time left to show the power of the idea in practice – I thought a wasted opportunity.

Spent a long time in the pub afterwards.


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