Dave, * Dave Page (dp...@pgadmin.org) wrote: > On Tue, Dec 5, 2017 at 11:01 PM, Bruce Momjian <br...@momjian.us> wrote: > > As part of PGConf.Asia 2017 in Tokyo, we had an unconference topic about > > zero-downtime upgrades. After the usual discussion of using logical > > replication, Slony, and perhaps having the server be able to read old > > and new system catalogs, we discussed speeding up pg_upgrade. > > > > There are clusters that take a long time to dump the schema from the old > > cluster and recreate it in the new cluster. One idea of speeding up > > pg_upgrade would be to allow pg_upgrade to be run in two stages: > > > > 1. prevent system catalog changes while the old cluster is running, and > > dump the old cluster's schema and restore it in the new cluster > > > > 2. shut down the old cluster and copy/link the data files > > When we were discussing this, I was thinking that the linking could be done > in phase 1 too, as that's potentially slow on a very large schema.
Right, I had that thought too when first reading this, but the problem there is that new files can show up due to a relation being extended (at least, and perhaps in other cases too..). > > My question is whether the schema dump/restore is time-consuming enough > > to warrant this optional more complex API, and whether people would > > support adding a server setting that prevented all system table changes? > > I've certainly heard of cases where pg_upgrade takes significant amounts of > time to run on very complex databases. Right, but that doesn't really answer the question as to which part of the pg_upgrade process is taking up the time. In any case, of course, if we're able to move part of what pg_upgrade does to be while the old server is online then that takes whatever the cost of that is out of the downtime window. The question is if that's a 5% improvement in the overall performance of pg_upgrade or a 70% one. This will be case-by-case, of course, but if, in the best-case, we only get a 5% improvement then this might not be worth the risk. Thanks! Stephen
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