On 21.03.24 17:58, Maxim Orlov wrote:
In commit 7b5275eec more tests and test coverage were added into
pg_resetwal/t/001_basic.pl <http://001_basic.pl>.
All the added stuff are pretty useful in my view. Unfortunately, there
were some magic constants
been used. In overall, this is not a problem. But while working on 64
bit XIDs I've noticed these
changes and spent some time to figure it out what this magic values are
stands fore.
And it turns out that I’m not the only one.
So, by Svetlana Derevyanko's suggestion, I made this patch. I add
constants, just like we did
in verify_heapam tests.
Consider this change:
-$mult = 32 * $blcksz / 4;
+$mult = SLRU_PAGES_PER_SEGMENT * $blcksz / MXOFF_SIZE;
with
+use constant SLRU_PAGES_PER_SEGMENT => 32;
+use constant MXOFF_SIZE => 4;
SLRU_PAGES_PER_SEGMENT is a constant that also exists in the source
code, so good.
But MXOFF_SIZE doesn't exist anywhere else. The actual formula uses
sizeof(MultiXactOffset), which isn't obvious from your patch. So this
just moves the magic constants around by one level.
The TAP test says
# these use the guidance from the documentation
and the documentation in this case says
SLRU_PAGES_PER_SEGMENT * BLCKSZ / sizeof(MultiXactOffset)
I think if we're going to add more symbols, then it has to be done
consistently in the source code, the documentation, and the tests, not
just one of them.
