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What is the overhead of RMAN hot backup (full backup including archive logs) being performed during business hours?

Does it actually affect the performance of the database?

What is the case when incremental backups are taken in terms of overhead?

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That depends on your disk subsystem.

A full backup is going to involve a metric crud-load of I/O (that is a technical term). That is going to put a huge load on your I/O subsystem. Depending on how I/O bound your system is, how much spare bandwidth your I/O subsystem has, how fast your I/O subsystem is, etc. the impact will range from "yeah, maybe it's a bit slower" to "everything times out, the system is unusable, users will be visiting the DBA team shortly with flaming pitchforks to express their displeasure."

I am hard-pressed to imagine a whole lot of situations where I'd ever want a full backup running on a non-trivial production database during anything close to business hours. If you have a real need to do this, I'd tend to be investigating things like DataGuard that would potentially allow you to offload the load of doing the backup to the standby database.

  • I'm in need to take incremental backup to bring my standby in sync with production. I have 3 DRs. Only one is lagging. Can I take incremental from another DR to do this? – tesla747 May 28 '16 at 5:03
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    Are you talking physical standbys? How is one lagging? Did you somehow lose an archived log that you have no backup for? If not, why aren't you bringing it up to date by applying archive logs? If it's been down for a days, restore from last night's backup and roll forward using archived logs. – Justin Cave May 28 '16 at 5:11
  • @tesla747 - Sorry, forgot to tag you in my earlier comment. – Justin Cave May 28 '16 at 5:31
  • Yes physical standby. It is lagging due to network disconnects. I will have to copy last night's full backup from prod to standby. – tesla747 May 28 '16 at 5:40
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    @tesla747 - If the network is not stable enough to transfer the archived logs, why would it be stable enough to transfer an entire backup? Surely transferring the full backup would cause many, many more disconnects. Why aren't you focusing on the fundamental problem of an unstable network and fixing that? – Justin Cave May 28 '16 at 5:50
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I confirm that a full or incremental backup during business hours can make your database inaccessible to end users and web services. Factors that can make things worse:

  • allocating too many channels to RMAN
  • using an out of support version like Oracle 10
  • having a database that is CPU or memory or network IO bound
  • running Dataguard at the same time
  • underlying network storage plays a huge part and can be the limiting factor for transfer rates

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