On 08/27/2014 09:53 AM, Andres Freund wrote:
>> > Perhaps instead of doing this in-core it would be better to make log 
>> > handling more extensible? I'm thinking add a specific "binary" format and 
>> > an external tool that can parse that and do whatever the user wants with 
>> > it. That means we don't have to keep adding more complexity to the 
>> > internal log handling (which already has the risk of being a bottleneck), 
>> > while allowing maximum user flexibility.
> There's a logging hook. Most of this should be doable from there.

Is there any docs at all on the logging hooks?  I couldn't find any.
Maybe that's why people keep trying to reinvent them.

The main reason I personally would like to have JSON logs has more to do
with formatting and extracting data.  For example, if you have a
prepared statement and log_min_duration_statement turned on, you get
something like this in the "message" and "details" fields:

"duration: 8.253 ms  execute <unnamed>: SELECT login FROM users WHERE id
= $1, "parameters: $1 = '90700'"

... and then for various analytics, like pgBadger and troubleshooting,
you have to break out the parts of those fields by regex and split,
which is error-prone; in our query replay tool, I have at least a dozen
commits tweaking the regexes because of some special case I didn't
account for (like an array parameter).

It would be vastly easier to work with the above as JSON:

"message" : { "duration" : 8.253, "command" : "execute",
"statement_name" : "<unnamed>", "statement" : "SELECT login FROM users
WHERE id = $1" }, "details" : { "parameters" : { "$1" : 90700 } }

This would allow me, or Dalibo, to remove literally dozens of lines of
error-prone regexing code.

That fix would, IMHO, make it worth enabling JSON logging as a logging
hook or something similar.  If we're just going to convert the CSV to
JSON, with the existing fields?  Waste of time, I can do that with a
5-line script in at least 3 different languages.

Josh Berkus
PostgreSQL Experts Inc.

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