Thread: clarify "rewritten" in pg_checksums docs
Hi, the pg_checksums docs mention that "When enabling checksums, every file in the cluster is rewritten". From IRC discussions, "rewritten" seems ambiguous, it could mean that a second copy of the file is written and then switched over, implying increased storage demand during the operation. So maybe "rewritten in-place" is better, as per the attached? Michael -- Michael Banck Projektleiter / Senior Berater Tel.: +49 2166 9901-171 Fax: +49 2166 9901-100 Email: michael.banck@credativ.de credativ GmbH, HRB Mönchengladbach 12080 USt-ID-Nummer: DE204566209 Trompeterallee 108, 41189 Mönchengladbach Geschäftsführung: Dr. Michael Meskes, Jörg Folz, Sascha Heuer Unser Umgang mit personenbezogenen Daten unterliegt folgenden Bestimmungen: https://www.credativ.de/datenschutz
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> On 1 Sep 2020, at 15:13, Michael Banck <michael.banck@credativ.de> wrote: > the pg_checksums docs mention that "When enabling checksums, every file > in the cluster is rewritten". > > From IRC discussions, "rewritten" seems ambiguous, it could mean that a > second copy of the file is written and then switched over, implying > increased storage demand during the operation. Makes sense, I can see that confusion. > So maybe "rewritten in-place" is better, as per the attached? Isn't "modified in-place" a more accurate description of the process? cheers ./daniel
Hi, Am Dienstag, den 01.09.2020, 15:29 +0200 schrieb Daniel Gustafsson: > > On 1 Sep 2020, at 15:13, Michael Banck <michael.banck@credativ.de> wrote: > > the pg_checksums docs mention that "When enabling checksums, every file > > in the cluster is rewritten". > > > > From IRC discussions, "rewritten" seems ambiguous, it could mean that a > > second copy of the file is written and then switched over, implying > > increased storage demand during the operation. > > Makes sense, I can see that confusion. > > > So maybe "rewritten in-place" is better, as per the attached? > > Isn't "modified in-place" a more accurate description of the process? AIUI we do rewrite the whole file (block by block, after updating the page header with the checksum), so yeah, I though about using modified instead but then decided rewritten is pretty (or even more) accurate. Michael -- Michael Banck Projektleiter / Senior Berater Tel.: +49 2166 9901-171 Fax: +49 2166 9901-100 Email: michael.banck@credativ.de credativ GmbH, HRB Mönchengladbach 12080 USt-ID-Nummer: DE204566209 Trompeterallee 108, 41189 Mönchengladbach Geschäftsführung: Dr. Michael Meskes, Jörg Folz, Sascha Heuer Unser Umgang mit personenbezogenen Daten unterliegt folgenden Bestimmungen: https://www.credativ.de/datenschutz
> On 1 Sep 2020, at 15:34, Michael Banck <michael.banck@credativ.de> wrote: > Am Dienstag, den 01.09.2020, 15:29 +0200 schrieb Daniel Gustafsson: >> Isn't "modified in-place" a more accurate description of the process? > > AIUI we do rewrite the whole file (block by block, after updating the > page header with the checksum), so yeah, I though about using modified > instead but then decided rewritten is pretty (or even more) accurate. Well, I was thinking less technically accurate and more descriptive for end users, hiding the implementation details. "Rewrite" sounds to me more like changing data rather than amending pages with a checksum keeping data intact. Either way, adding "in-place" is an improvement IMO. cheers ./daniel
On Tue, Sep 01, 2020 at 03:44:06PM +0200, Daniel Gustafsson wrote: > Well, I was thinking less technically accurate and more descriptive for end > users, hiding the implementation details. "Rewrite" sounds to me more like > changing data rather than amending pages with a checksum keeping data intact. > Either way, adding "in-place" is an improvement IMO. Using rewritten still sounds more adapted to me, as we still write the thing with chunks of size BLCKSZ. No objections with the addition of "in-place" for that sentence. Any extra opinions? -- Michael
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On Wed, Sep 02, 2020 at 05:26:16PM +0900, Michael Paquier wrote: > Using rewritten still sounds more adapted to me, as we still write the > thing with chunks of size BLCKSZ. No objections with the addition of > "in-place" for that sentence. Any extra opinions? Seeing no objections, I have applied the original patch of this thread down to 12. -- Michael