Hello,
I think that pgstattuple should use PageGetExactFreeSpace() instead of
PageGetHeapFreeSpace() or PageGetFreeSpace(). The latter two compute the
free space minus the space of a line pointer. They are used like this in
the rest of the code (heapam.c):
pagefree = PageGetHeapFreeSpace(page);
if (newtupsize > pagefree) { we need a another page for the tuple }
... so it makes sense to take the line pointer into account in this context.
But it in the pgstattuple context, I think we want the exact free space.
I have attached a patch.
Best regards,
FrédéricFrom 350abec004fe472922800135d5d94ca3d8212da4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fr=C3=A9d=C3=A9ric=20Yhuel?= <frederic.yh...@dalibo.com>
Date: Wed, 21 Aug 2024 15:05:11 +0200
Subject: [PATCH] pgstattuple: use PageGetExactFreeSpace()
instead of PageGetHeapFreeSpace() and PageGetFreeSpace()
We want the exact free space, we don't care if there's enough room for
another line pointer.
---
contrib/pgstattuple/pgstatapprox.c | 2 +-
contrib/pgstattuple/pgstatindex.c | 2 +-
contrib/pgstattuple/pgstattuple.c | 6 +++---
3 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/contrib/pgstattuple/pgstatapprox.c b/contrib/pgstattuple/pgstatapprox.c
index c84c642355..a27dea621e 100644
--- a/contrib/pgstattuple/pgstatapprox.c
+++ b/contrib/pgstattuple/pgstatapprox.c
@@ -111,7 +111,7 @@ statapprox_heap(Relation rel, output_type *stat)
* treat them as being free space for our purposes.
*/
if (!PageIsNew(page))
- stat->free_space += PageGetHeapFreeSpace(page);
+ stat->free_space += PageGetExactFreeSpace(page);
else
stat->free_space += BLCKSZ - SizeOfPageHeaderData;
diff --git a/contrib/pgstattuple/pgstatindex.c b/contrib/pgstattuple/pgstatindex.c
index 5c06ba6db4..1b6b768cf8 100644
--- a/contrib/pgstattuple/pgstatindex.c
+++ b/contrib/pgstattuple/pgstatindex.c
@@ -311,7 +311,7 @@ pgstatindex_impl(Relation rel, FunctionCallInfo fcinfo)
max_avail = BLCKSZ - (BLCKSZ - ((PageHeader) page)->pd_special + SizeOfPageHeaderData);
indexStat.max_avail += max_avail;
- indexStat.free_space += PageGetFreeSpace(page);
+ indexStat.free_space += PageGetExactFreeSpace(page);
indexStat.leaf_pages++;
diff --git a/contrib/pgstattuple/pgstattuple.c b/contrib/pgstattuple/pgstattuple.c
index 3bd8b96197..7e2a7262a3 100644
--- a/contrib/pgstattuple/pgstattuple.c
+++ b/contrib/pgstattuple/pgstattuple.c
@@ -372,7 +372,7 @@ pgstat_heap(Relation rel, FunctionCallInfo fcinfo)
buffer = ReadBufferExtended(rel, MAIN_FORKNUM, block,
RBM_NORMAL, hscan->rs_strategy);
LockBuffer(buffer, BUFFER_LOCK_SHARE);
- stat.free_space += PageGetHeapFreeSpace((Page) BufferGetPage(buffer));
+ stat.free_space += PageGetExactFreeSpace((Page) BufferGetPage(buffer));
UnlockReleaseBuffer(buffer);
block++;
}
@@ -385,7 +385,7 @@ pgstat_heap(Relation rel, FunctionCallInfo fcinfo)
buffer = ReadBufferExtended(rel, MAIN_FORKNUM, block,
RBM_NORMAL, hscan->rs_strategy);
LockBuffer(buffer, BUFFER_LOCK_SHARE);
- stat.free_space += PageGetHeapFreeSpace((Page) BufferGetPage(buffer));
+ stat.free_space += PageGetExactFreeSpace((Page) BufferGetPage(buffer));
UnlockReleaseBuffer(buffer);
block++;
}
@@ -565,7 +565,7 @@ pgstat_index_page(pgstattuple_type *stat, Page page,
{
OffsetNumber i;
- stat->free_space += PageGetFreeSpace(page);
+ stat->free_space += PageGetExactFreeSpace(page);
for (i = minoff; i <= maxoff; i = OffsetNumberNext(i))
{
--
2.39.2
