On 06/16/2015 02:04 AM, Michael Paquier wrote:
In order to reduce the risk of failure to a minimum and to preserve the performance of the tool when using --source-server, I think that we should add some check using pg_stat_file to see if a file is still present or not, and if it is missing we can safely skip it thanks to minRecoveryPoint. Now the problem is that pg_stat_file fails automatically if the file targeted is missing. Hence, to avoid a bunch of round trips with the server with one call to pg_stat_dir per file, I think that we should add some if_not_exists option to pg_stat_file, defaulting to false, to skip the error related to the file missing and have it return NULL in this case. Then we could use this filter on the file path in libpq_executeFileMap() to fetch only the file chunks that actually exist on the server.
You'll also need to add the option to pg_read_binary_file, though, because even if you do a test with pg_stat_file() just before reading the file, there's a race condition: someone might still delete file between pg_stat_file() and pg_read_file().
Listing the directories with pg_ls_dir() has the same problem. As does pg_tablespace_location().
Note that we could as well use some plpgsql-ing to do the same, but the extension of pg_stat_file looks more useful to me. Thoughts?
Hmm. You'll need to add the option to all of those functions. Maybe it's nevertheless the simplest approach.
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