On 2016-08-29 18:22:56 +0300, maksim wrote:
Now I complete extension that provides facility to see the current state of
query execution working on external session in form of EXPLAIN ANALYZE
output. This extension works on 9.5 version, for 9.6 and later it doesn't
support detailed statistics for parallel nodes yet.

Could you expand a bit on what you want this for exactly?

Max goal - to push my extension to postgres core. But now it's ready only for 9.5. Prerequisites of this extension are patches presented here.

2. Patch that enables to interrupt the query executor
This patch enables to hang up hooks on executor function of each node
(ExecProcNode). I define hooks before any node execution and after
I use this patch to add possibility of query tracing by emitted rows from
any node. I interrupt query executor after any node delivers one or zero
rows to upper node. And after execution of specific number trace steps I can
get the query state of traceable backend which will be somewhat
deterministic. I use this possibility for regression tests of my extension.

This will increase executor overhead.

In simple case we have checks on existence of hooks. We may suppose to use only not heavy processing on hooks under regular execution of query. In my case (query trace), I set up hooks under trace mode and throw off otherwise.

> I think we'll need to find a way
> to hide this behind the existing if (instrument) branches.

And so can be. It doesn't matter for trace mode. But I think instrument branch is intended only for collecting statistics by nodes.

3. Patch that enables to output runtime explain statistics
This patch extends the regular explain functionality. The problem is in the
point that regular explain call makes result output after query execution
performing InstrEndLoop on nodes where necessary. My patch introduces
specific flag *runtime* that indicates whether we explain running query and
does some insertions in source code dedicated to output the statistics of
running query.

Unless I'm missing something this doesn't really expose a user of this

This patch is only for extension. As described in https://www.postgresql.org/message-id/CACACo5Sz7G0MFauC082iM=xx_hq7qq5ndr4jpo+h-o5vp6i...@mail.gmail.com regular ExplainNode() prints only statistics after query execution and asserts under InstEndLoop(). My patch releases this problem and rewrite formulas for statistic parameters appropriate to running queries without affecting regular EXPLAIN outputs.

Maksim Milyutin
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company

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