On Mon, Mar 17, 2014 at 10:20 AM, Robert Haas <robertmh...@gmail.com> wrote: > 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.
+1, too. And, what about making pg_copy call posix_fadvise(DONT_NEED) against the archived file after the copy? Also It might be good idea to support the direct copy of the file to avoid wasting the file cache. Regards, -- Fujii Masao -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
