| From: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
|---|---|
| To: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, ilsa(at)ilsadee(dot)com, pgsql-docs(at)lists(dot)postgresql(dot)org |
| Subject: | Re: What does "Table rewrite" mean? |
| Date: | 2018-01-21 03:47:50 |
| Message-ID: | 20180121034750.cgfugcqbgnxxm3lg@alvherre.pgsql |
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| Thread: | |
| Lists: | pgsql-docs |
Michael Paquier wrote:
> On Fri, Jan 19, 2018 at 11:33:43AM -0500, Tom Lane wrote:
> > It means reading the whole table and writing it out in some modified
> > form (for instance, with some column transformed into a new datatype).
> > It's not "dangerous" in any way ... but if you've got many GB of data in
> > the table and you can't afford to have the table locked for a long time,
> > then it's something to avoid.
>
> Yeah that can be costly. Note that WAL corresponding to this data needs
> to be generated as well.
Maybe we need to document this somewhere, particularly now that we have
a "table_rewrite" event item.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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