Re: Gratuitous use of savepoint considered silly, if not harmful

[Melvin Davidson <melvin6925@xxxxxxxxx>]

On Fri, Apr 13, 2018 at 2:32 PM, Jerry Sievers <gsievers19@xxxxxxxxxxx> wrote:

So I'm (was) puzzled here when a big warehouse system just upgraded to
9.6 which I knew does only a few 100k *real* transactions/day was
wrapping txid_current() so fast, in turn causing some big, nasty tablesl
to age and then require painful long-running vacuums...

Got the brilliant idea to full statement log for just 20 minutes or so
and then do some digging.

OMG my DW team's Pentaho/Kettle driver gizmo emulates single-line
autocommit inserts using savepoints.

It racked up ~1.8M txids meanwhile actually doing only ~900
transactions.

Symptomatic of this also is that your pg_stat_database.(xact_commit +
xact_rollback) counter over time will be wildly smaller then the
advancement of txid_current() perhaps helping in the confusion.

This was csvlogged and field #8 is command-tag which we're pulling out

and summarizing as seen below.

tmp$ grep ^2018 $log-file | grep silly_etl_user | cut -d, -f8 | sort | uniq -c | sort -k1,1bnr -k2

1880283 "INSERT"
1879931 "RELEASE"
1879931 "SAVEPOINT"
 314838 "SELECT"
 314298 "UPDATE"
   2681 "idle"
   2677 "authentication"
   1967 "SET"
    898 "COMMIT"
    897 "BEGIN"
    160 "DELETE"
     83 "TRUNCATE TABLE"
      6 "DROP TABLE"
      2 "CREATE INDEX"
      2 "CREATE TABLE AS"

Anyway, I felt this was worth sharing :-)

Thx

--
Jerry Sievers
Postgres DBA/Development Consulting
e: postgres.consulting@comcast.net
p: 312.241.7800

 

As Forest Gump once said "Stupid is as stupid does". 😁

--

Melvin Davidson
Maj. Database & Exploration Specialist
Universe Exploration Command – UXC
Employment by invitation only!