Re: Buffer usage in EXPLAIN and pg_stat_statements (review)

Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> 1. I would suggest something like "Blocks
> Read: %ld Hit: %ld Temp Read: %ld\n". See the way we handle output
> of sort type and space usage, for example.

I have some questions:
* Did you use single space and double spaces in your example intentionally?
* Should we use lower cases here?
* Can I use "temp" instead of "Temp Read" to shorten the name?

> 2. Similarly, in pg_stat_statements, the Counters structure could
> easily use the same names for the structure members that we already
> use in e.g. pg_stat_database - blks_hit, blks_read, and, say,
> blks_temp_read. In fact I tend to think we should stick with "blocks"
> rather than "buffers" overall, for consistency with what the system
> does elsewhere.

I agree to rename them into blks_*, but EXPLAIN (blocks) might be
misleading; EXPLAIN (buffer) can be interpreted as "buffer usage",
but normally we don't call it "block usage".

My suggestion is:
* EXPLAIN (buffers) prints (blocks read: %ld hit: %ld temp: %ld)
* auto_explain.log_buffers are not changed
* pg_stat_statements uses blks_hit and blks_read

> 4. "Instrumentation stack is broken" doesn't seem terribly helpful in
> understanding what has gone wrong.

This message is only for hackers and should not occur.
Assert() might be ok instead.

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center