Le mar. 6 nov. 2018 12:40 PM, Tom Lane <t...@sss.pgh.pa.us> a écrit :
> Ravi Krishna <srkrish...@aol.com> writes: > > I loaded 133 million rows to a wide table (more than 100 cols) via COPY. > The table has > > no index at this time. Since I am the only user I don't see any other > activity. > > Now when I run select count(*) on the table where I just loaded data, it > runs for ever, > > more than 10min and still running. Intrigued, I checked locks and saw > nothing. Then I noticed something > > strange. When select count(*) runs, PG is writing to wal_logs, and that > too a large amount. Why? > > That represents setting the yes-this-row-is-committed hint bits on the > newly loaded rows. The first access to any such row will set that bit, > whether it's a select or a VACUUM or whatever. > > regards, tom lane > And IIRC, it can generate a high WAL traffic since the first page change after a checkpoint is done with full page write. And you said that it's happening on a big table with wide rows.... >
