| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, Stephen Frost <sfrost(at)snowman(dot)net>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Tom Kincaid <tomjohnkincaid(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Masahiko Sawada <masahiko(dot)sawada(at)2ndquadrant(dot)com> |
| Subject: | Re: storing an explicit nonce |
| Date: | 2021-05-27 16:31:23 |
| Message-ID: | 20210527163123.7a4lu3a3ieewi3k2@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2021-05-27 10:47:13 -0400, Robert Haas wrote:
> Now, another option is to do what you suggest here. We could say that
> if a dirty page is evicted, but the page is only dirty because of
> hint-type changes, we don't actually write it out. That does avoid
> using the same nonce for multiple writes, because now there's only one
> write. It also fixes the problem on standbys that Andres was
> complaining about, because on a standby, the only way a page can
> possibly be dirtied without an associated WAL record is through a
> hint-type change.
What does that protect against that I was concerned about? That still
allows hint bits to be leaked, via
1) replay WAL record with FPI
2) hint bit change during read
3) incremental page change
vs 1) 3). Even if we declare that OK, it doesn't actually address the
whole issue of WAL replay not necessarily re-creating bit identical page
contents.
Greetings,
Andres Freund
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