Horton

Re: storing an explicit nonce

Bruce Momjian <bruce@momjian.us>

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From: Bruce Momjian <bruce@momjian.us>
To: Stephen Frost <sfrost@snowman.net>
Cc: Robert Haas <robertmhaas@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Masahiko Sawada <sawada.mshk@gmail.com>, Tom Kincaid <tomjohnkincaid@gmail.com>, Andres Freund <andres@anarazel.de>, Amit Kapila <amit.kapila16@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Masahiko Sawada <masahiko.sawada@2ndquadrant.com>
Date: 2021-05-26T01:51:31Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Rethink method for assigning OIDs to the template0 and postgres DBs.

  2. pg_upgrade: Preserve database OIDs.

  3. pg_upgrade: Preserve relfilenodes and tablespace OIDs.

  4. Fix for new Boolean node

  5. Improve error handling of HMAC computations

  6. Add macro RelationIsPermanent() to report relation permanence

  7. Enhance nbtree index tuple deletion.

On Tue, May 25, 2021 at 09:42:48PM -0400, Stephen Frost wrote:
> The nonce needs to be a new one, if we include the hint bits in the set
> of data which is encrypted.
> 
> However, what I believe folks are getting at here is that we could keep
> the LSN the same, but increase the nonce when the hint bits change, but
> *not* WAL log either the nonce change or the hint bit change (unless
> it's being logged for some other reason, in which case log both), thus
> reducing the amount of WAL being produced.  What would matter is that
> both the hint bit change and the new nonce hit disk at the same time, or
> neither do, or we replay back to some state where the nonce and the hint
> bits 'match up' so that the page decrypts (and the integrity check
> works).

How do we prevent torn pages if we are writing the page with a new
nonce, and no WAL-logged full page image?

> That generally seems pretty reasonable to me and basically makes the
> increase in nonce work very much in the same manner that the hint bits
> themselves do- sometimes it changes even when the LSN doesn't but, in
> such cases, we don't actually WAL it, and that's ok because we don't
> actually care about it being updated- what's in the WAL when the page is
> replayed is perfectly fine and we'll just update the hint bits again
> when and if we decide we need to based on the actual visibility
> information at that time.

We get away with this because hint-bit only changes only change single
bytes on the page, and we can't tear a page between bytes, but if we
change the nonce, the entire page will have different bytes.  What am I
missing here?

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  If only the physical world exists, free will is an illusion.