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Re: pg_dump transaction's read-only mode

From: Gurjeet Singh <singh(dot)gurjeet(at)gmail(dot)com>
To: Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>
Cc: Stephen Frost <sfrost(at)snowman(dot)net>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: pg_dump transaction's read-only mode
Date: 2013-01-09 01:12:34
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Lists: pgsql-hackers
On Mon, Dec 31, 2012 at 1:38 AM, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>wrote:

> On Sun, Dec 30, 2012 at 12:38 AM, Stephen Frost <sfrost(at)snowman(dot)net>
> wrote:
> > * Pavan Deolasee (pavan(dot)deolasee(at)gmail(dot)com) wrote:
> >> On Fri, Sep 7, 2012 at 6:06 PM, Kevin Grittner
> >> > That makes sense to me.  The reason I didn't make that change when I
> >> > added the serializable special case to pg_dump was that it seemed
> >> > like a separate question; I didn't want to complicate an already big
> >> > patch with unnecessary changes to non-serializable transactions.
> >> >
> >>
> >> If we agree, should we change that now ?
> >
> > This is on the next commitfest, so I figure it deserves some comment.
> > For my part- I tend to agree that we should have it always use a read
> > only transaction.  Perhaps we should update the pg_dump documentation to
> > mention this as well though?  Pavan, do you want to put together an
> > actual patch?
> >
> I'd posted actual patch on this thread, but probably linked wrong
> message-id in the commitfest page. Will check and correct. Regarding
> pg_dump's documentation, I don't have strong views on that. Whether
> pg_dump runs as a read-only transaction or not is entirely internal to
> its implementation, but then if we make this change, it might be worth
> telling users that they can trust that pg_dump will not make any
> changes to their database and hence a safe operation to carry out.

I have updated the commitfest submission to link to the correct patch email.

I initially thought that this patch deserves accompanying documentation
because pg_dump's serializable transaction may error out because of a
conflict. But the following line in the docs [1] confirms otherwise:

"read-only transactions will never have serialization conflicts"

So no doc patch necessary :)

Gurjeet Singh

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