| From: | "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com> |
|---|---|
| To: | 'Julien Rouhaud' <rjuju123(at)gmail(dot)com> |
| Cc: | Michael Paquier <michael(at)paquier(dot)xyz>, Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>, "Jamison, Kirk" <k(dot)jamison(at)jp(dot)fujitsu(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | RE: reloption to prevent VACUUM from truncating empty pages at the end of relation |
| Date: | 2019-02-22 02:38:56 |
| Message-ID: | 0A3221C70F24FB45833433255569204D1FB9F614@G01JPEXMBYT05 |
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From: Julien Rouhaud [mailto:rjuju123(at)gmail(dot)com]
> FWIW, I prefer shrink over truncate, though I'd rather go with
> vacuum_shink_enabled as suggested previously.
Thanks. I'd like to leave a committer to choose the name. FWIW, I chose shrink_enabled rather than vacuum_shrink_enabled because this property may be used in other shrink situations in the future. What I imagined was that with the zheap, DELETE or some maintenance operation, not vacuum, may try to shrink the table. I meant this property to indicate "whether this table shrinks or not" regardless of the specific operation that can shrink the table.
> I'm not sure that I get this comment. Since both require a
> ShareUpdateExclusiveLock, you can't change the parameter while a
> VACUUM is active on that table. Did you wanted to use another lock
> mode?
No, changing the parameter acquires ShareUpdaeExclusive lock. I just imitated the description for n_distinct in the same comment block. The meaning is that the setting cannot be changed during VACUUM, so in-flight VACUUM is not affected.
Regards
Takayuki Tsunakawa
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