"68.4. Visibility Map" change suggestion.
The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/12/storage-vm.html
Description:
Currently the documentation lists the line below;
`Each heap relation has a Visibility Map (VM) to keep track of which pages
contain only tuples that are known to be visible to all active
transactions;`
Should it instead read like;
`Each heap relation has a Visibility Map (VM) to keep track of only those
pages that contain tuples known to be visible to all active transactions;`
After reading through the documentation and reading the first line, I first
thought that VM only kept track of pages that only had visible tuples.
Instead my understanding is that it shows which pages have any visible
tuples in them.
On Mon, 2021-04-26 at 21:55 +0000, PG Doc comments form wrote:
The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/12/storage-vm.html
Description:Currently the documentation lists the line below;
`Each heap relation has a Visibility Map (VM) to keep track of which pages
contain only tuples that are known to be visible to all active
transactions;`Should it instead read like;
`Each heap relation has a Visibility Map (VM) to keep track of only those
pages that contain tuples known to be visible to all active transactions;`After reading through the documentation and reading the first line, I first
thought that VM only kept track of pages that only had visible tuples.
Instead my understanding is that it shows which pages have any visible
tuples in them.
I think that the wording of the documentation is more correct.
The VM also tracks the pages that are not all-visible. They have the
corresponding bit set to 0.
Yours,
Laurenz Albe