On 09/01/2015 11:55 AM, Krishnan Parthasarathi wrote:
----- Original Message -----
hi,
Afr needs context based defaults for quorum where by default
quorum value is 'none' for 2-way replica and 'auto' for 3 way replica.
Anuradha sent http://review.gluster.org/11872 to fix the same. May be we
can come up with more generic solution. The present solution remembers
the default in volinfo->options and also written to the store. So the
default will be shown in "volume info" output and if we want to change
the defaults in future we will need to carefully think of all the things
that could go wrong especially peers getting rejected because of the
md5sum mismatch. Another way to solve the same problem is to generate
the default value of the vme-option based on the context of the volume
when we have to write to the volfile. In this particular case, we need
to generate default as 'none' for 2-way-replica-count volume. and 'auto'
for 3-replica-count volume. For volume-get command handling also we need
to consider this dynamic default value. For implementing this, we can
add a new member 'context_based_default_value_get()'(please feel free to
come up with better name for the function :-) ) to the vme-table which
can be invoked to get the default option which takes the volinfo as
parameter at least, and not set .value i.e implicitly .value will be NULL.
This is based on earlier design detail in the comment of vme-table:
* Fourth field is <value>. In this context they are used to specify
* a default. That is, even the volume dict doesn't have a value,
* we procced as if the default value were set for it.
We just want to enhance the existing behavior with this proposed change.
It seems more generic than the present solution in the patch. In future
people can write their own implementations of context based default
value generation following same procedure. Let me know your comments.
Here are a few things that are not clear to me.
1) Does the context-based default value for an option comes into effect
only when .value in vme table is NULL?
If there is context based default then the static default value should
be NULL is my feeling.
2) IIUC, the generated default value is applied to the volume files generated
and persisted no place else. Is this correct?
Yes.
3) What happens if the context_based_default_get() is not available in all
glusterds in the cluster? e.g, upgrade from 3.6 to 3.7.x (where this may land).
Shouldn't this behaviour also be 'versioned' to prevent different volume files
being served by different nodes of the cluster?
In the context_based_default_value_get() we can add the version checks
and generate it the way we want.
Pranith
Pranith
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