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We hit a problem previous weeks related Exadata storage. In fact not related to Exadata but the impact is big.
We are using Attunity Replicate for a CDC tool and Attunity Replicate CDC method is different from goldengate.
As you know Goldengate uses the stream for reading redo logs and archives. But Attunity Replicate is different.
(I will use shortcut AR for Attunity replicate)
AR is reading online redo logs and archive logs with Oracle DBMS package so it may be affected by disk IO or anything else.
Solution:
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Another story that;
Disk scrubbing is a new feature that introduced in Oracle 11.2.0.4 and Exadata 11.2.3.3.0 storage.
Disk scrubbing checks the disks for the corruption risks.
In default configuration,checks every 2 weeks.(hardDiskScrubInterval=biweekly)
Let me show;
It is the default configuration
CellCLI> list cell attributes name,hardDiskScrubInterval
x6celadm05 biweekly
Till this step, everything is ok, Oracle protects our disks and data. But every cells start scrubbing same time, you may have IO problem.
Our database has a lot of transactions, but we don't see any impact of this scrubbing, till AR went slow done(latency is growing) while scrubbing is continues.
After we found the scrubbing information from cell alert logs, we decide to start scrubbing different times. Then we set a different start time
for every cell.
For example;
One cell disk scrubbing takes 44 hours and we have 7 cells. So I didn't change the interval(biweekly). After Cell 1 disk scrubbing is finished,
cell 2 will start, after cell 2 is finished cell 3 will start etc. So in this method, only one cell will do scrubbing in a meantime.
dcli -g cell_group -l root cellcli -e "list cell attributes name,hardDiskScrubInterval,hardDiskScrubStartTime"
x6celadm07: x6celadm07 biweekly 2018-04-22T05:00:00+03:00
x6celadm06: x6celadm06 biweekly 2018-04-20T08:00:00+03:00
x6celadm05: x6celadm05 biweekly 2018-04-18T11:00:00+03:00
x6celadm04: x6celadm04 biweekly 2018-04-16T14:00:00+03:00
x6celadm03: x6celadm03 biweekly 2018-04-14T17:00:00+03:00
x6celadm02: x6celadm02 biweekly 2018-04-12T20:00:00+03:00
x6celadm01: x6celadm01 biweekly 2018-04-10T23:00:00+03:00
After this implementation, AR(attunnity replicate) latencies was going down.
