EXPLAIN BUFFERS

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

> In this case, I think that the auto_explain changes out to be part of
> the same patch as the core EXPLAIN changes

Here is a rewritten patch to add EXPLAIN (ANALYZE, BUFFERS) and
support for it by contrib/auto_explain. I removed pg_stat_statements
support from the patch for now.

I modifed heavily in buffer statistics conters; These counters are
put all together into struct BufferUsage. The struct is also used in
struct Instrumentation. The global buffer usage counters are saved
into 'bufusage_start' field at the InstrStartNode(), and accumulated
into 'bufusage' field and global counters are reset at InstrStopNode().

EXPLAIN BUFFERS only shows 'hit', 'read' and 'temp read' in text format
to fit in display, but xml or json format contains all of them.

I removed ShowBufferUsage() because we can retrieve the same information
from xml or json explain output, but the patch does not drop
log_statement_stats variable families nor ShowUsage() functions.
We could also remove all of them if no one use them at all.

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