On Sun, Mar 16, 2014 at 6:23 AM, MauMau <maumau...@gmail.com> wrote: > The PostgreSQL documentation describes cp (on UNIX/Linux) or copy (on > Windows) as an example for archive_command. However, cp/copy does not sync > the copied data to disk. As a result, the completed WAL segments would be > lost in the following sequence: > > 1. A WAL segment fills up. > > 2. The archiver process archives the just filled WAL segment using > archive_command. That is, cp/copy reads the WAL segment file from pg_xlog/ > and writes to the archive area. At this point, the WAL file is not > persisted to the archive area yet, because cp/copy doesn't sync the writes. > > 3. The checkpoint processing removes the WAL segment file from pg_xlog/. > > 4. The OS crashes. The filled WAL segment doesn't exist anywhere any more. > > Considering the "reliable" image of PostgreSQL and widespread use in > enterprise systems, I think something should be done. Could you give me > your opinions on the right direction? Although the doc certainly escapes by > saying "(This is an example, not a recommendation, and might not work on all > platforms.)", it seems from pgsql-xxx MLs that many people are following > this example. > > * Improve the example in the documentation. > But what command can we use to reliably sync just one file? > > * Provide some command, say pg_copy, which copies a file synchronously by > using fsync(), and describes in the doc something like "for simple use > cases, you can use pg_copy as the standard reliable copy command."
+1. This won't obviate the need for tools to manage replication, but it would make it possible to get the simplest case right without guessing. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers