HAWQ-1373 - Added feature to reload GUC values using hawq reload-config

[outofmem0ry]

This commit introduces hawq reload-config <object> as a replacement of hawq stop <object> -u|--reload, to reload GUC values without restarting the cluster.

[outofmem0ry]

Scoped out some documentation changes which are detailed below -

Files with hawq stop cluster -u
Files with hawq stop cluster --reload
Files with references to reload

[linwen]

Shubham, I think what you've done in this PR is to add a command for hawq, which can reload GUC configs without restarting the system. Currently, this is done by this command "hawq stop cluster --reload", which is a little bit ambiguous in my opinion. So if we all agree on using "hawq reload-config" instead, the old codes related to this reloading GUC logic should be removed. @radarwave @vVineet

[stanlyxiang]

If we add "hawq reload-config", I think there is no need for "hawq stop cluster -u". 2 commands have same function make me more confused.

[radarwave]

Thanks @outofmem0ry to contribute this, please check below comments.

1. I think we should keep the legacy command to do reload in case it's hard coded in some user cases, print a deprecated message should be fine.
2. Make sure all the related help messages and documents are updated.
3. Chose a proper name for this option before user start to use it, 'reload' or 'reload-config' or something else?
4. Add test for this option.

[outofmem0ry]

@linwen @stanlyxiang @radarwave - Thank you for the comments and suggestions.

@radarwave - Please see the comments inline

1. I think we should keep the legacy command to do reload in case it's hard coded in some user cases, print a deprecated message should be fine.

The change that is committed prints a message as seen below and exits. I can change the message and let the command continue.

hawq stop cluster -u
To reload GUC values without restarting hawq cluster use 'hawq reload-config <object>'

2. Make sure all the related help messages and documents are updated.

This is something that will go into incubator-hawq-docs and am working on scoping the change for this.

3. Chose a proper name for this option before user start to use it, 'reload' or 'reload-config' or something else?

reload sounds good. Also, am open for any other suggestions

4. Add test for this option.

Sure, let me see how we plug test into the codebase. Any pointers are appreciated.

[outofmem0ry]

@radarwave - am in the process of making final changes for this pull request, I don't see any existing test infrastructure for management utilities, am I missing something here. Can you point me to some existing test cases and how they are plugged into hawq code base.

[radarwave]

@outofmem0ry
Please check the cases in below folder as example:
incubator-hawq/src/test/feature/ManagementTool

[outofmem0ry]

@radarwave committed the final changes, doc changes pending. Will submit a PR in docs repo.

[radarwave]

Need to fix:
run 'hawq reload' without any other arguments:

hawq reload
Traceback (most recent call last):
File "/usr/local/hawq/bin/hawq", line 215, in
main()
File "/usr/local/hawq/bin/hawq", line 135, in main
sub_args_list.append("-u")
UnboundLocalError: local variable 'sub_args_list' referenced before assignment
Traceback (most recent call last):
File "/usr/local/hawq/bin/hawq", line 215, in
main()
File "/usr/local/hawq/bin/hawq", line 135, in main
sub_args_list.append("-u")
UnboundLocalError: local variable 'sub_args_list' referenced before assignment

[radarwave]

This deprecation message is not align with other messages.
Run 'hawq stop cluster -u' then you can see.

[outofmem0ry]

@radarwave - I deliberately kept the messages printing different so that it is noticeable to the user, as it is a deprecation warning.

[radarwave]

Typo 'valueof'.

[outofmem0ry]

Thank you for pointing it out, will correct it.

[outofmem0ry]

@radarwave - Fixed and incorporated above comments.

[radarwave]

LGTM +1

[linwen]

+1

[radarwave]

Thanks for @outofmem0ry 's contribution, I have squashed and merged this commit. Please close this PR.

Welcome to do more contributions.

[outofmem0ry]

Thank you @linwen @radarwave . Closing this PR, will also submit a PR for documentation changes to apache/incubator-hawq-docs repo.