Le mar. 6 nov. 2018 12:40 PM, Tom Lane <tgl@sss.pgh.pa.us> a écrit :
Ravi Krishna <srkrishna1@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....
