it is the commit call to postgres that suddently takes more time than normal(as observed for other inserts)
it seems as if postgres does some activity (on its own) after some installs.
thats why i have observed this pattern ....i.e. commit taking less time for some installs (eg 1000) ..then suddently becoming high an dthen dropping back ....
then again takes normal time for another 1000 ...and again becomes high (for 6 - 7 intstalls).