Track transaction time

[smcgivern]

I'm not sure if this is the correct way to track it (on the server, with an always-outdated timestamp), but I couldn't see an obvious way to track this on the client side, and logically a transaction must be tied to a particular server connection, right? Now tracking on the client side.

Closes #114 (total_query_time is already implemented).

[smcgivern]

This is failing in CI:

  1) Stats SHOW STATS clients connect and make one query updates *_query_time and *_wait_time
     Failure/Error: expect(results["total_xact_time"].to_i).to be_within(200).of(750)
       expected 1203 to be within 200 of 750
     # ./stats_spec.rb:32:in `block (4 levels) in <top (required)>'

It passes locally for me inside the dev container, but I wonder if that shows that this approach is flawed.

Having said that, I do see other specs fail some of the time, like this, which I don't think I broke:

  1) Stats SHOW POOLS bad database name does not change any stats
     Failure/Error: expect(results["sv_idle"]).to eq("1")

       expected: "1"
            got: "2"

       (compared using ==)
     # ./stats_spec.rb:72:in `block (4 levels) in <top (required)>'

[drdrsh]

I am testing this with

pgbench -i
pgbench -c 5 -j 10 -T 1800 -P 10 -S

and seeing monotonically increasing avg transaction time.

I am trying to figure out the reason for it, also I would expect the tests to fail so we probably have a coverage gap here that we'll want to address

[smcgivern]

Ha, yes, this is definitely wrong. I added a test that runs more queries (not in a transaction), and it fails with:

  1) Stats SHOW STATS clients connect and make one query updates *_query_time and *_wait_time
     Failure/Error: expect(results["total_xact_time"].to_i).to be_within(200).of(750)
       expected 51397 to be within 200 of 750
     # ./stats_spec.rb:50:in `block (4 levels) in <top (required)>'

When this metric should not have increased in that time.

[smcgivern]

This was already the case, and is the same as PgBouncer: https://github.com/pgbouncer/pgbouncer/blob/e2a2a682fe9069366fca970ec2492d774b4f6b40/test/test_admin.py#L74-L75

[smcgivern]

@drdrsh could you try again, please? I'm seeing an issue when running pgbench in the dev container where both avg_query_time and avg_xact_time are zero, and I'm not sure if I'm doing something wrong in the setup there. (I don't think I broke it in this PR as I see the same on the main branch.)