Обсуждение: PostgreSQL Dump based backup using pipe

Am 2015-05-27 13:19, schrieb girish R G peetle:
[...]
> 2. On Linux also from strace output of pg_dump -Fc (compressed dump)
> used with fifo file, I see illegal seek performed on fifo file too. 
> But restore doesnt have any issues. Is  it safe to use pg_dump -Fc
> with output file as fifo on Linux ?

I have used  pg_dump -Fc with fifos on both Linux and BSDs for several
years without any problem, afair.

Jan

girish R G peetle <giri.anamika0@gmail.com> writes:
> We were using named pipe to read dump data from 'pg_dump -Fc' (compressed
> format) on Windows.
> Restore was failing with 'corrupt dump data' error.
> Later found that pg_dump was performing 'illegal seek' on pipe to write the
> data, which was causing corrupt dump.

That should work.  What PG version are you using exactly, and can we see a
full example of what you were trying to do?

There are unsupported cases --- I recall in particular that you can't do
a parallel restore from a pipe --- but you should not be getting "corrupt
file" errors.

            regards, tom lane

girish R G peetle <giri.anamika0@gmail.com> writes:
> Thanks for checking. Here is the details.
> PostgreSQL Version - 9.2.8

Hm.  A quick trawl of the git logs didn't find any relevant bug fixes
since 9.2.8.

> Dump command : pg_dump.exe -U postgres -Fc -b test

> Platform : Windows Server 2008 R2

> Output of dump command is redirected to write end of named pipe.

I'm suspicious that that's exposing you to Windows' infamous text-mode
data mangling.  You might try using "-f namedpipe" instead of a shell
redirect.

            regards, tom lane

girish R G peetle <giri.anamika0@gmail.com> writes:
> I just tracked pg_dump writing output to a file. (using procmon)
> As indicated below data is not written in serial fashion.
> If we use name pipe would this behavior cause problem ?

It's less efficient with a named pipe, yes, because then pg_dump
can't do that.  But this doesn't prove anything one way or another
concerning your original complaint.

            regards, tom lane

On May 28, 2015, at 11:58 AM, girish R G peetle <giri.anamika0@gmail.com> wrote:
>
> If pipe is used…

You’re assuming that it writes to files and writes to pipes the same way. That is not a valid assumption.


--
Scott Ribe
scott_ribe@elevated-dev.com
http://www.elevated-dev.com/
https://www.linkedin.com/in/scottribe/
(303) 722-0567 voice