Proposal: add encode_time to LogEntry

[ruslandoga]

Right now LogEntry includes decode_time but no encode_time. I wonder why and if it's OK to add encode_time to the logs.

I think meter = event(meter, :encode) can be added to encode and maybe_encode similar to https://github.com/elixir-ecto/db_connection/blob/285650ee8bbcea119ac74327b81f2571a42eedc0/lib/db_connection.ex#L1350 and then calculated similar to https://github.com/elixir-ecto/db_connection/blob/285650ee8bbcea119ac74327b81f2571a42eedc0/lib/db_connection/log_entry.ex#L62-L64

This metric would be useful in ClickHouse-like adapters that occasionally perform large INSERTs. Separating the encoding time from network latency there allows for better insight on where time is spent and what should be optimised.

[josevalim]

Encoding happens outside of db_connection, which is why it isn't measured here.

[ruslandoga]

Sorry for a dumb question, but what does "outside" mean in this context?

[josevalim]

No dumb question at all. It means db_connection is not the one doing the encoding. It already receives encoded data!

[josevalim]

The important bit is that encoding is done outside of the connection process (for performance) and decoding is partially done inside the connection process.

[ruslandoga]

Ah, I think I understand. DBConnection.Query.encode and decode are called outside of checkout. I think what confuses me is that handle_execute (which is wrapped in checkout) does not seem to be called in the connection process either -- it's called in the caller process similar to encode and decode. But even then, what stops us from recording encode times? It doesn't seem like process dict or anything tied to a process is used for storing metrics, and when encode happens, there's already access to meter.

[josevalim]

Sorry, the word process was misleading there. Very little happens in the connection process. It is mostly there to hold the connection when no-one is using, handle idle checks, and timeouts. A better way to say is that it happens while we own the connection.