>Von: pgsql-performance-owner@xxxxxxxxxxxxxx [pgsql-performance-owner@xxxxxxxxxxxxxx]" im Auftrag von "Claudio Freire [klaussfreire@xxxxxxxxx] >Gesendet: Freitag, 18. Juli 2014 01:21 >An: Chris Ruprecht >Cc: pgsql-performance@xxxxxxxxxxxxxx >Betreff: Re: [PERFORM] Building multiple indexes on one table. > >On Thu, Jul 17, 2014 at 7:47 PM, Chris Ruprecht <chris@xxxxxxxxxxx> wrote: >> Is there any way that I can build multiple indexes on one table without having to scan the table multiple times? For small tables, that's probably not an issue, but if I have a 500 GB table that I need to create 6 indexes on, I don't want to read that table 6 times. >> Nothing I could find in the manual other than reindex, but that's not helping, since it only rebuilds indexes that are already there and I don't know if that reads the table once or multiple times. If I could create indexes inactive and then run reindex, which then reads the table once, I would have a solution. But that doesn't seem to exist either. > >Just build them with separate but concurrent connections, and the >scans will be synchronized so it will be only one. > >Btw, reindex rebuilds one index at a time, so what I do is issue >separate reindex for each index in parallel, to avoid the repeated >scans as well. > >Just make sure you've got the I/O and CPU capacity for it (you'll be >writing many indexes at once, so there is a lot of I/O). Index creation on large tables are mostly CPU bound as long as no swap occurs. I/O may be an issue when all your indexes are similar; e.g. all on single int4 columns. in other cases the writes will not all take place concurrently. To reduce I/O due to swap, you can consider increasing maintenance_work_mem on the connextions/sessionns that build the indexes. regards, Marc Mamin
