[SERVER-19483] Allow querying wiredTigerEngineRuntimeConfig via getParameter Created: 19/Jul/15  Updated: 12/Oct/17  Resolved: 02/Oct/17

Status: Closed
Project: Core Server
Component/s: Storage
Affects Version/s: 3.0.4
Fix Version/s: 3.6.0-rc0

Type: Improvement Priority: Major - P3
Reporter: Andre de Frere Assignee: Daniel Gottlieb (Inactive)
Resolution: Done Votes: 7
Labels: NewEng
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Related
related to SERVER-29290 Report all current configuration opti... Backlog
related to SERVER-16019 Add special WT_CONNECTION::reconfigu... Closed
Backwards Compatibility: Fully Compatible
Sprint: Storage 2017-10-02, Storage 2017-10-23
Participants:
Case:

 Description   

setting the wiredTigerEngineRuntimeConfig string in the shell, at the command line or in a config file does not change the config string when viewed through getParameter.

> db.adminCommand( { setParameter : 1, "wiredTigerEngineRuntimeConfig" : "cache_size=2GB" })
{ "was" : "", "ok" : 1 }
> db.adminCommand( { getParameter : "1", wiredTigerEngineRuntimeConfig : 1  } )
{ "wiredTigerEngineRuntimeConfig" : "", "ok" : 1 }



 Comments   
Comment by Githook User [ 02/Oct/17 ]

Author:

{'email': 'daniel.gottlieb@mongodb.com', 'name': 'Daniel Gottlieb', 'username': 'dgottlieb'}

Message: SERVER-19483: Have getParameter on wiredTigerEngineRuntimeConfig return the last value set from a client.
Branch: master
https://github.com/mongodb/mongo/commit/113b4fa007f638675586203fb5a9e735bcff36f5

Comment by Daniel Gottlieb (Inactive) [ 29/Sep/17 ]

Pinging andre.defrere dmitry.agranat

Comment by Daniel Gottlieb (Inactive) [ 28/Sep/17 ]

Hi alexander.gorrod andre.defrere dmitry.agranat, I'm looking into this ticket.

I have a patch up that simply has getParameter on the runtime config return the last string successfully set. The last string set is also returned in the "was" field on followup setParameter calls.

From my understanding, WiredTiger would still require changes to be able to ask it about settings dictated by other mechanisms.

Otherwise, is a change of this form agreeable? Or should the ticket be put back into the backlog?

Comment by Alexander Gorrod [ 27/Jun/17 ]

Could you elaborate how extracting the WiredTiger parameters through the command line can result in unexpected and undesired behavior?

The places it has caused problems in the past is when configuration options are removed in more recent releases (which breaks applications that are explicitly setting them), or when default settings change and existing applications don't get the benefit from the change because they are explicitly using the old value.

This is one of the goals of this ticket, to extract the defaults from a system which are deployed now.

I thought the goal was to extract the content of the user specified wiredTigerEngineRuntimeConfig setting.

Comment by Alexander Gorrod [ 26/Jun/17 ]

we want the entire WiredTiger engine configuration including WT's defaults. Assuming this will include wiredTigerEngineRuntimeConfig and all the hidden parameters.

That hasn't been what is wanted in the past. The defaults can change between releases, and including them in a string returned to the user can result in unexpected and undesired behavior. Are you sure that's what is being requested?

Comment by David Hows [ 21/Jun/17 ]

Its worth noting here that MongoDB has a number of default configuration options set when using WiredTiger.

It would be valuable to understand the use-case for this option so we know what to return.
Do we want the entire WiredTiger engine configuration including WT's defaults?
Do we want the entire config string most recently passed through to WiredTiger including MongoDB's defaults?
Do we just want the most recent config string passed in by the user showing only the changes the user has made?

Comment by Ramon Fernandez Marina [ 05/Aug/15 ]

According to the description of this feature in SERVER-16019 there's currently no way to query WiredTiger runtime settings, so getParameter will always return an empty string. Repurposing this ticket as an enhancement request to enable querying WiredTiger settings via getParameter.

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