On Wed, 23 Mar 2016, singh.janmejay wrote:
Foreach can only work with arrays as of now. It can't work with
objects (key-value pairs). So [{name: ... value: ...}, {..},...] is
the only format that will work as of now.
We can enhance foreach to work with objects.
I can make a flag available at dyn-stats bucket level, which can
control serialization format, but that would really be a hack.
From single-responsibility pattern pov, impstats should be the only
component that decides how to layout data for user to see.
How about this:
impstats(format="json" wrapDynamicObjects="on"...)?
It defaults to off, which keeps backward compatibility.
So what do you guys think about:
- wrapDynamicObjects="on|off"
- generating [{name: a, value: 10}, {...} ...] vs. {a: 10, ...}
(foreach will handle the former out of the box, but later is concise,
readable and light-weight in addition to being more json-y.
- enhancing foreach to work with {a: 10, b: 20...}
If we can enhance foreach to work with the concise format, I would rather wait
for it instead of introducing the wrapping version.
I'm thinking that foreach walks through arrays, rather than mixing concepts, a
foreachobject that gives us a name and contents for a {} list of objects may be
the right thing to do?
foreach just returns a single object while foreachobject needs to return the
object and name.
although, if we ever get the ability to address arrays directly, being able to
look at the array position would be the equivalent of the name.
David Lang
On Wed, Mar 23, 2016 at 12:26 AM, David Lang <[email protected]> wrote:
On Tue, 22 Mar 2016, singh.janmejay wrote:
How about this: we support a new flag in impstats which allows
json-formatted stats-line to optionally use
encapsulated/wrapped-layout?
impstats(format="json" ...) generates
{"name":"msg_per_host","origin":"dynstats.bucket","z-scribe1r-b":80,"SWEB10":67}
however,
impstats(format="json/w" ...) generates {"header":
{"name":"msg_per_host","origin":"dynstats.bucket"}, "counters" :
{"z-scribe1r-b":80,"SWEB10":67}}
This is relevant, the serilization format we use right now mixes
pre-defined keys with counter-names and it can affect regular static
counters too.
with the existing pstats output, there is no ability for user-defined data
to become a tag name, so there is no potential for ambiguity. but with
dynastats, this is not a possibility, and the format we use should prevent
problems.
Also, just from a conceptual point of view, why should the bucket contents
be at the same level as the bucket name?
other than backwards compatibility, what advantage is there of the current
version in JSON? the documentation uses the plain text equivalant, which is
perfectly legitimate because there is an order to the line, and after you
get past the name and origin, everything else on the line is name-value
pairs of counters, again, no ambiguity.
But with JSON, I don't believe that you can depend on tools maintaining (or
even identifying) the order of the elements, and if you have multiple
elements with the same name, it's implementation dependent as to which one
will be seen.
So purely from a correctness and defensive programming point of view, I
think the current JSON serialization should be changed, with the old format
no longer being an option.
As to the details of the new format
What I'm wanting to do with the counters is something like
if $!origin == "dynstats.bucket" then {
foreach $.tag $!counters {
/var/log/stats;format
}
}
to output one line per counter.
I'm very flexible in how to do this, but I would much rather be able to do
this inside rsyslog than have to serialize things to an external script,
have it parse the json and process it.
my initial thinking was just do
counters: [ "z-scribe1r-b":80,"SWEB10":67 ]
but as I'm typing this, I realize that doesn't work as I don't have a way to
break $.tag down to reference the name and the value.
I'd hate to have to do something like
counters: [{"name":"z-scribe1r-b","value":80 },{"name":"SWEB10","value":67}]
this mirrors the misuse of XML that gives it such a horrible reputation. But
unless we introduce some new function to rsyslog to break things down, I
don't see a better way. If we do need to do something like this, I sure
would not want to make it the default JSON, which would result in two
different formats. I hate the idea of starting to have different formats
because of subtypes of data (what is someone wants the cee version of this
for example, you start to have orthoginal format decisions)
David Lang
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