Re: EXPLAIN BUFFERS

Here is an updated patch per discussion.

  * Counters are accumulative. They contain I/Os by child nodes.
  * Text format shows all counters.
  * Add "shared_" prefix to variables representing shared buffers/blocks.

Euler Taveira de Oliveira <euler@timbira.com> wrote:

> Itagaki Takahiro escreveu:
> > I think the current output is enough and useful in normal use.
> > We can use XML or JSON format for more details.
> > 
> I don't think it is a good idea to have different information in different
> formats. I'm with Robert; *don't* do that.

I'm afraid of the human-unreadability of the text format, that is discussed
in the YAML format thread. ...but I found we say the following in the docs.

  XML or JSON output contains the same information as the text output format
  http://developer.postgresql.org/pgdocs/postgres/sql-explain.html

Obviously I should not hide any information only in the text format.
The new output will be: (in one line)
  Shared Blocks: (hit=2 read=1641 written=0) Local Blocks: (hit=0 read=0 written=0) Temp Blocks: (read=1443 written=1443)

> There are nodes that don't read or write blocks.

This will be impossible now because we re-defined the meaning of counters
as "accumulated number of I/O". Even if the node never read or write blocks,
it might contain some child nodes with I/O.

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