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From Lisa Owen <lo...@pivotal.io>
Subject HAWQ server configuration parameters (GUCs)
Date Thu, 19 Jan 2017 17:28:25 GMT
hi hawq developers,

i have been looking at src/backend/utils/misc/guc.c to try to get a better
understanding of hawq server configuration parameters (GUCs) and how they
are exposed to end users and developers.  i have initially focused on GUCs
with config groups labeled "DEVELOPER_OPTIONS", "DEFUNCT_OPTIONS",
"DEPRECATED_OPTIONS", and "PRESET_OPTIONS".

i have some general questions regarding these GUC config groups:
  1.  which GUCs and their values should be displayed/changeable via "hawq
config" command?
  2.  which of the GUCs are updatable, which are read-only?
  3.  which of the GUCs should be documented to the end user, and if/how to
"flag them"?

DEVELOPER_OPTIONS - it appears we expose some developer GUCs to the
end-user.  what does it mean for a GUC to be a developer option?  (when)
should developer options be displayed in "hawq config -l" output?  (when)
should developer GUCs be discussed in the docs?  it seems we are somewhat
inconsistent in these areas.  many, but not all, of the GUCS labeled as
"DEVELOPER_OPTIONS" are also identified as "GUC_NO_SHOW_ALL", which
generally excludes them from "hawq_config -l" output.  the documentation
currently describes a few of the developer GUCs.  if we are describing
developer GUCs in end-user documentation, should we be flagging them as
such?

DEFUNCT_OPTIONS - the GUCs labeled "DEFUNCT_OPTIONS" are pretty
straightforward from an external perspective - none of them are currently
documented, and none show up in "hawq config -l" output.

DEPRECATED_OPTIONS - GUCs that are part of the "DEPRECATED_OPTIONS" config
group are functioning, but not recommended for use.  some are documented,
some are not.  should we be explicitly identifying deprecated GUCs as such
in the documentation?  should we even be documenting them at all?  should
the values of deprecated GUCs show up in "hawq config -l" output?

PRESET_OPTIONS - some of the GUCS labeled with "PRESET_OPTIONS" are
identified as read-only in the documentation.  i used hawq config to change
one of them, "hawq config -c block_size -v 32768", and the operation
apparently worked (i.e. no error returned).  so, what does it mean for a
GUC to be preset?  read-only?  are they all read-only?  some appear to be
recognized by "hawq config -c" command, while others are not.

i've pulled together a spreadsheet identifying the "DEVELOPER_OPTIONS",
"DEFUNCT_OPTIONS", "DEPRECATED_OPTIONS", and "PRESET_OPTIONS" GUCs and
whether or not:
    - the GUC is documented in the current HAWQ docs
    - the GUC and associated value show up in "hawq config -l" output (when
run by superuser)
and other notes.

thanks for any clarity you can provide on which of these GUCs we should be
exposing to the end user.


-lisa

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