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My change request to patch 3 SQL instances on the same server was denied because of one instance - they say a server reboot is fine, but not a few hours downtime.

Seeing as each instance is standalone, should it not be fine to patch 2 instances and leave the third?

I see there is a 'shared components' feature - what is this exactly, is this down for all instances during the patching, and does it matter?

How can I assuage the fears of my colleagues that the third instance will still be working - the business are not willing for it to go down even for a couple of hours in the evening.

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Firstly, it always better to test patches in DEV environment before applying on Production.

To answer, there won't be downtime/interruption for Instance 3 while patching/removing path on Instance 1, all you need select particular instance during the wizard or command line as follows:

KBXXXX.exe /qs /IAcceptSQLServerLicenseTerms /Action=Patch /InstanceName=Intance1

There might be restart required (manual restart) to proceed with Instance 2 patching after completing instance 1.

Shared features are updated (patched) once. In your case during the Instance 1 or which ever starts first, and not applied while patching other instances on the same server. We never experienced any interruption with shared features (considered following): But if you got Integration Services and it's heavily used you must find maintenance windows where it's got less overhead.

  1. Client Tools Connectivity
  2. Client Tools Backward Compatibility

My environment was 3 instances on 1 server, all of them are AG replicas. One primary other two secondary, and there are 3 servers total with same configuration.

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  • Not exactly related to the question, but, besides the possibility of applying patches on one instance while the others are online, what are the advantages of having 3 instances with AG replicas on the same box? I've never used AG myself and this particular detail of your answer (which I think was helpful) caught my attention.
    – Ronaldo
    Oct 22, 2019 at 17:17
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    Hi @Ronaldo, of course, my words doesn't mean all of them are part of same AG. My bad, i could have mention that. it's like this: there are 3 servers, each one hosts 3 replicas, 1 replica in each server is primary and other 2 are secondaries.
    – Shekar Kola
    Oct 22, 2019 at 17:29
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If each instance and the application(s) using it are just relying on the database engine, then upgrading each instance should not affect the others at all unless a reboot is needed (and usually for a SQL patch or service pack only restarting the relevant SQL services is needed, not a full machine reboot).

See https://learn.microsoft.com/en-us/sql/sql-server/install/feature-selection for a list of features. Most of the shared components are application or client tier parts so even if the apps are using them they may not be using them on this server (instead having them installed elsewhere and using them to connect to instances on this server).

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