Re: [HACKERS] strange behavior of UPDATE

Edmund Mergl <E(dot)Mergl(at)bawue(dot)de> writes:
> The table is filled with 1.000.000 rows of random data
> and on every field an index is created.

BTW, do you happen to know just how random the data actually is?
I noticed that the update query
update bench set k500k = k500k + 1 where k100 = 30;
updates 10,000 rows. If this "random" data actually consists of
10,000 repetitions of only 100 distinct values in every column,
then a possible explanation for the problem would be that our
btree index code isn't very fast when there are large numbers of
identical keys. (Mind you, I have no idea if that's true or not,
I'm just trying to think of likely trouble spots. Anyone know
btree well enough to say whether that is likely to be a problem?)

regards, tom lane