RE: dbms_diskgroup read very slow on exa

Culprits most likely are network latency and competition for the devices you are trying to read, along with a few technical details of the connection dealt with in the context of old golden gate by Alex Fatkulin eleven years ago in this blog: https://blog.pythian.com/oracle-goldengate-extract-internals-part-ii/  

10 MBPS unmolested also seems like you might have a per session wire limit of 10 MBPS somewhere in your technical stack.  

I don’t know Attunity well enough to know whether there is a read local archivelog from the file system option.  

IF there is, my suggestion would be to make an additional archivelog destination local to the place Attunity is running and use that local option to read the archived redologs copy at which will then have no ASM competition from production processes, and which will end the per ingestor network latency and bandwidth requirements in favor of moving the archived redolog copy unidirectionally exactly once.  

I hope this helps.  

mwf  

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Laurentiu Oprea Sent: Tuesday, March 23, 2021 7:22 AM
To: ORACLE-L (oracle-l_at_freelists.org) Subject: dbms_diskgroup read very slow on exa  

Hello all,  

I received complaints about Attunity doing the ingestion very slowly. The way is configured is to connect directly to ASM instance and get the archivelog files.This is an exa X7  

My observations wre:

-> is using dbms_diskgroup.read to perform the reads from asm

-> mainly the wait time is ASM Fixes Package I/O (and some CPU)

-> Is using 16 sessions distributed over 2 nodes each reading with an estimate speed (based on ASH numbers) of around 10MBPS

-> in case a smart scan starts (for example smart incremental backup) the I/O speed of these sessions drops to around 1MBPS

-> session level stats shows a very low number for "cell flash cache read hits" so looks like all reads are from spinning disks
 

To me it looks like the reading speed even in normal conditions(without heavy competition) is very low, can someone help me with some hints on what can be the culprit?  

Thank you.

--
http://www.freelists.org/webpage/oracle-l