[Engine-devel] Using config values

[Mike Kolesnik]

----- Original Message -----

> ----- Original Message -----

> > From: "Mike Kolesnik" <mkolesni at redhat.com>
> 
> > To: "Kanagaraj" <kmayilsa at redhat.com>
> 
> > Cc: "engine-devel" <engine-devel at ovirt.org>
> 
> > Sent: Sunday, December 1, 2013 8:08:42 AM
> 
> > Subject: Re: [Engine-devel] Using config values
> 

> > ----- Original Message -----
> 

> > > Hi All,
> > 
> 
> > Hi Kanagaraj,
> 

> > > The are some issues arising in configurations whenever we move up on the
> > > versions(3.3 => 3.4), because of the way we store and interpret them.
> > 
> 

> > > Whenever there is a new cluster level, you will need to add a new entry
> > > for
> > > all(most) of the configuration. Mostly a copy paste if you see from 3.2
> > > to
> > > 3.3, except some CPU/PM type related configurations.
> > 
> 
> > > Better option would be to have the defaul config value in
> > > ConfigValues.java
> > > and the overrides will go to config.sql. In this approach you don't need
> > > a
> > > new entries to config.sql when there is a new cluster level.
> > 
> 

> > > Lets take an exmaple, "SupportForceCreateVG" - This is supported from 3.1
> > > onwards,
> > 
> 

> > > If you look at config.sql, you will see following entries
> > 
> 
> > > select fn_db_add_config_value('SupportForceCreateVG','false','3.0');
> > 
> 
> > > select fn_db_add_config_value('SupportForceCreateVG','true','3.1');
> > 
> 
> > > select fn_db_add_config_value('SupportForceCreateVG','true','3.2');
> > 
> 
> > > select fn_db_add_config_value('SupportForceCreateVG','true','3.3');
> > 
> 

> > > And in ConfigValues.java
> > 
> 

> > > @TypeConverterAttribute(Boolean.class)
> > 
> 
> > > @DefaultValueAttribute("false")
> > 
> 
> > > SupportForceCreateVG,
> > 
> 

> > > Now if there is 3.4 and 3.5, the user needs to add 2 more entries, which
> > > i
> > > feel is redundant.
> > 
> 

> > > Instead we can make
> > 
> 

> > > @TypeConverterAttribute(Boolean.class)
> > 
> 
> > > @DefaultValueAttribute("true")
> > 
> 
> > > SupportForceCreateVG,
> > 
> 

> > > and have only the following in config.sql
> > 
> 
> > > select fn_db_add_config_value('SupportForceCreateVG','false','3.0');
> > 
> 

> > > if a particular value(for a specific cluster level) is not found in
> > > Config.sql, the fallback is to use the value available in
> > > ConfigValues.java.
> > 
> 
> > This has already been implemented, there are many "feature supported"
> > configurations working like this (for example GlusterSupport).
> 

> > I think a more interesting approach would be to move these out of the DB
> > since these values don't really hav e a reson to be there.
> 
> > Since the entire thing is abstracted by "Gluster/FeatureSupported" classes
> > then we can easily change mechanism (of course whatever code is not using
> > it
> > can be easily converted to use the mechanism)
> 

> > For example a simple enum could do the trick:
> 
> > ------------------------------------- EXAMPLE
> > -------------------------------------
> 
> > /**
> 
> > * Convenience class to check if a gluster feature is supported or not in
> > any
> > given version.<br>
> 
> > * Methods should be named by feature and accept version to check against.
> 
> > */
> 
> > public class GlusterFeatureSupported {
> 
> > /**
> 
> > * @param version
> 
> > * Compatibility version to check for.
> 
> > * @return <code>true</code> if gluster support is enabled,
> > <code>false</code>
> > if it's not.
> 
> > */
> 
> > public static boolean gluster(Version version) {
> 
> > return SupportedFeatures.GLUSTER.isSupportedOn(version);
> 
> > }
> 

> > /**
> 
> > * @param version
> 
> > * Compatibility version to check for.
> 
> > * @return <code>true</code> if gluster heavyweight refresh is enabled,
> > <code>false</code> if it's not.
> 
> > */
> 
> > public static boolean refreshHeavyWeight(Version version) {
> 
> > return SupportedFeatures.REFRESH_HEAVYWEIGHT.isSupportedOn(version);
> 
> > }
> 

> > /* More methods... */
> 

> > enum SupportedFeatures {
> 
> > GLUSTER(Version.v3_0),
> 
> > REFRESH_HEAVYWEIGHT(Version.v3_0, Version.v3_1),
> 
> > /* More members */;
> 

> > private Set<Version> unsupportedVersions = new HashSet<Version>();
> 

> > private SupportedFeatures(Version... versions) {
> 
> > unsupportedVersions.addAll(Arrays.asList(versions));
> 
> > }
> 

> > public boolean isSupportedOn(Version version) {
> 
> > return !unsupportedVersions.contains(version);
> 
> > }
> 
> > }
> 
> > ------------------------------------- END EXAMPLE
> > -------------------------------------
> 

> > Thoughts?
> 

> unless i didn't understand something, this is not good,
> this should stay configurable by the users,
> for example if some user experience some issues with a feature and want to
> turn it off/change the values..
> (not all version configuration are boolean, some are different values to
> different versions, like cpu-list)

This is for API level compatibility. 
If VDSM doesn't support for example hot plug in 3.1 then the user can't just decide that it does and change it. 
Also, this is not changeable by user since it's not exposed by engine-config (nor should it be). 

This is strictly for the engine-VDSM API compatibility, not for other configs which are version specific. 

> > Regards,
> 
> > Mike
> 

> > > Please share your thoughts on this.
> > 
> 

> > > Thanks,
> > 
> 
> > > Kanagaraj
> > 
> 

> > _______________________________________________
> 
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> 
> > Engine-devel at ovirt.org
> 
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> 
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