pg_stat_transaction patch

Hi,

I propose a set of new statistics functions and system views.

I need these functions in order to do automated testing of our system,
consisting of hundreds of stored procedures in plpgsql.
My plan is to develop some additional functions to pgTAP, benefiting from
the new system tables I've added.

The patch should apply to 9.0beta or HEAD, but I created it using 8.4.3
because that's the version I'm using.

I'm thankful for your feedback.

My apologies if the packaging of the patch does not conform to your
guidelines, feedback on this is also welcome.

--
Best regards,

Joel Jacobson
Glue Finance

E: jj(at)gluefinance(dot)com
T: +46 70 360 38 01

Postal address:
Glue Finance AB
Box 549
114 11 Stockholm
Sweden

Visiting address:
Glue Finance AB
Birger Jarlsgatan 14
114 34 Stockholm
Sweden

README:

Background
==========
The views pg_stat_user_tables and pg_stat_user_functions shows statistics on
tables and functions.
The underlying functions named pg_stat_get_* fetches recent data from the
statistics collector, and returns the requested value for the given "oid"
(i.e. "tableid/relationid" or "functionid").
In the end of each transaction[1], the collected statistics are sent to the
statistics collector[2].

[1] upon COMMIT/ROLLBACK, or a bit later (the report frequency is controlled
by the PGSTAT_STAT_INTERVAL setting, default value is 500 ms)
[2] if you do a ps aux, it is the process named "postgres: stats collector
process"

Problem
=======
Within a current transaction, there was no way of accessing the internal
data structures which contains the so far collected statistics.
I wanted to check exactly what data changes my functions made and what
functions they called, without having to commit the transaction
and without mixing the statistics data with all the other simultaneously
running transactions.

Solution
========
I have exported get accessor methods to the internal data structure
containing so far collected statistics for the current transaction.

I have also exported the method pgstat_report_stat to make it possible to
force a "report and reset" of the so far collected statistics.
This was necessary to avoid not-yet-reported statistics for a previous
transaction to affect the current transaction.

I used the unused_oids script to find unused oids and choosed the range
between 3030-3044 for the new functions.

Functions
=========
test=# \df+ pg_catalog.pg_stat_get_transaction_*

List of functions
Schema | Name | Result data type
| Argument data types | Type | Volatility | Owner | Language |
Source code | Description

------------+--------------------------------------------+------------------+---------------------+--------+------------+-------+----------+--------------------------------------------+-------------------------------------------------------------------------
pg_catalog | pg_stat_get_transaction_blocks_fetched | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_blocks_fetched | statistics: number of blocks
fetched in current transaction
pg_catalog | pg_stat_get_transaction_blocks_hit | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_blocks_hit | statistics: number of blocks
found in cache in current transaction
pg_catalog | pg_stat_get_transaction_dead_tuples | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_dead_tuples | statistics: number of dead
tuples in current transaction
pg_catalog | pg_stat_get_transaction_function_calls | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_function_calls | statistics: number of function
calls in current transaction
pg_catalog | pg_stat_get_transaction_function_self_time | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_function_self_time | statistics: self execution time
of function in current transaction
pg_catalog | pg_stat_get_transaction_function_time | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_function_time | statistics: execution time of
function in current transaction
pg_catalog | pg_stat_get_transaction_live_tuples | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_live_tuples | statistics: number of live
tuples in current transaction
pg_catalog | pg_stat_get_transaction_numscans | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_numscans | statistics: number of scans
done for table/index in current transaction
pg_catalog | pg_stat_get_transaction_tuples_deleted | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_tuples_deleted | statistics: number of tuples
deleted in current transaction
pg_catalog | pg_stat_get_transaction_tuples_fetched | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_tuples_fetched | statistics: number of tuples
fetched by idxscan in current transaction
pg_catalog | pg_stat_get_transaction_tuples_hot_updated | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_tuples_hot_updated | statistics: number of tuples
hot updated in current transaction
pg_catalog | pg_stat_get_transaction_tuples_inserted | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_tuples_inserted | statistics: number of tuples
inserted in current transaction
pg_catalog | pg_stat_get_transaction_tuples_returned | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_tuples_returned | statistics: number of tuples
read by seqscan in current transaction
pg_catalog | pg_stat_get_transaction_tuples_updated | bigint
| oid | normal | stable | joel | internal |
pg_stat_get_transaction_tuples_updated | statistics: number of tuples
updated in current transaction
(14 rows)

I also had to create a new internal function, "get_funcstat_entry".
This function find or create a PgStat_BackendFunctionEntry entry for the
given oid (functionid).
The name and behaviour is similar to the existing function
"get_tabstat_entry".

System views
============
pg_stat_transaction_tables - shows so far collected table statistics for the
current transaction (almost identical structure as pg_stat_user_tables, but
lacks the last_* columns)
pg_stat_transaction_functions - shows so far collected function statistics
for the current transaction (identical structure as pg_stat_user_functions)

Test/Use case
=============

Patched files
=============
/doc/src/sgml/monitoring.sgml
/src/backend/catalog/system_views.sql
/src/backend/postmaster/pgstat.c
/src/backend/utils/adt/pgstatfuncs.c
/src/include/catalog/pg_proc.h
/src/include/pgstat.h