BUG #6463: tables can have at most 1600 columns

I drop a column but Postgresql still shows old (deleted) columns...

My Java program does this:
drop a boolean column and then add same column (with same name and
specification), in dozens times, because updating (this) column is very slow
!!!
AND finally it says "tables can have at most 1600 columns"

Sorry, this is not a bug, or at least we're not going to fix it.
The fact that DROP COLUMN doesn't physically remove the column is an
intentional design decision. If we didn't do it that way, dropping
a column would require rewriting the entire table (and all its indexes)
and so would be horribly slow.

Perhaps if you discussed why you think that repeatedly dropping and
re-adding a column is a useful thing to do, we could help you find
another way. The bugs list is not the place for that discussion,
however.

regards, tom lane