On Fri, Feb 21, 2025 at 11:17 AM Melanie Plageman
<melanieplageman@gmail.com> wrote:
> [v31-0001-Delay-extraction-of-TIDBitmap-per-page-offsets.patch]
Nice patch, seems like a straightforward win with the benefits you
explained: less work done under a lock, less work done in the second
iterator if the rest of this stuff doesn't make it in yet, and less
space used assuming it does. My only comment is that I'm not sure
about this type:
+/*
+ * The tuple OffsetNumbers extracted from a single page in the bitmap.
+ */
+typedef OffsetNumber TBMOffsets[TBM_MAX_TUPLES_PER_PAGE];
It's used for a stack object, but it's also used as a degraded pointer here:
+extern void tbm_extract_page_tuple(TBMIterateResult *iteritem,
+
TBMOffsets offsets);
Maybe a personal style question but degraded pointers aren't my
favourite C feature. A couple of alternatives, I am not sure how good
they are: Would this output variable be better wrapped up in a new
struct for better API clarity? If so, shouldn't such a struct also
hold ntuples itself, since that really goes with the offsets it's
holding? If so, could iteritem->ntuples then be replaced with a
boolean iteritem->lossy, since all you really need to be able to check
is whether it has offsets to give you, instead of using -1 and -2 for
that? Or as a variation without a new struct, would it be better to
take that output array as a plain pointer to OffsetNumber and
max_offsets, and return ntuples (ie how many were filled in, cf commit
f6bef362), for the caller to use in a loop or stash somewhere, with an
additional comment that TBM_MAX_TUPLES_PER_PAGE is guaranteed to be
enough, for convenience eg for arrays on the stack?
