On Mon, Sep 09, 2024 at 06:25:07PM +0300, Nazir Bilal Yavuz wrote:
> On Thu, 5 Sept 2024 at 18:54, Noah Misch <[email protected]> wrote:
> > On Thu, Sep 05, 2024 at 03:59:53PM +0300, Nazir Bilal Yavuz wrote:
> > > On Wed, 4 Sept 2024 at 21:43, Noah Misch <[email protected]> wrote:
> > > > https://postgr.es/m/caeudqaozv3wty5tv2t29jcwpydbmkbiwqkzd42s2ogzdixp...@mail.gmail.com
> > > > then observed that collect_corrupt_items() was now guaranteed to never
> > > > detect
> > > > corruption. I have pushed revert ddfc556 of the pg_visibility.c
> > > > changes. For
> > > > the next try, could you add that testing we discussed?
> > >
> > > Do you think that corrupting the visibility map and then seeing if
> > > pg_check_visible() and pg_check_frozen() report something is enough?
> >
> > I think so. Please check that it would have caught both the blkno bug and
> > the
> > above bug.
>
> The test and updated patch files are attached. In that test I
> overwrite the visibility map file with its older state. Something like
> this:
>
> 1- Create the table, then run VACUUM FREEZE on the table.
> 2- Shutdown the server, create a copy of the vm file, restart the server.
> 3- Run the DELETE command on some $random_tuples.
> 4- Shutdown the server, overwrite the vm file with the #2 vm file,
> restart the server.
> 5- pg_check_visible and pg_check_frozen must report $random_tuples as
> corrupted.
Copying the vm file is a good technique. In my test runs, this does catch the
"never detect" bug, but it doesn't catch the blkno bug. Can you make it catch
both? It's possible my hand-patching to recreate the blkno bug is what went
wrong, so I'm attaching what I used. It consists of
v1-0002-Use-read-stream-in-pg_visibility-in-collect_corru.patch plus these
fixes for the "never detect" bug from your v6-0002:
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -724,4 +724,4 @@ collect_corrupt_items(Oid relid, bool all_visible, bool
all_frozen)
{
- bool check_frozen = false;
- bool check_visible = false;
+ bool check_frozen = all_frozen;
+ bool check_visible = all_visible;
Buffer buffer;
@@ -757,5 +757,5 @@ collect_corrupt_items(Oid relid, bool all_visible, bool
all_frozen)
*/
- if (all_frozen && !VM_ALL_FROZEN(rel, blkno, &vmbuffer))
+ if (check_frozen && !VM_ALL_FROZEN(rel, blkno, &vmbuffer))
check_frozen = false;
- if (all_visible && !VM_ALL_VISIBLE(rel, blkno, &vmbuffer))
+ if (check_visible && !VM_ALL_VISIBLE(rel, blkno, &vmbuffer))
check_visible = false;
diff --git a/contrib/pg_visibility/pg_visibility.c
b/contrib/pg_visibility/pg_visibility.c
index 773ba92..ac575a1 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -41,6 +41,20 @@ typedef struct corrupt_items
ItemPointer tids;
} corrupt_items;
+/*
+ * Helper struct for read stream object used in
+ * collect_corrupt_items() function.
+ */
+struct collect_corrupt_items_read_stream_private
+{
+ bool all_frozen;
+ bool all_visible;
+ BlockNumber blocknum;
+ BlockNumber nblocks;
+ Relation rel;
+ Buffer *vmbuffer;
+};
+
PG_FUNCTION_INFO_V1(pg_visibility_map);
PG_FUNCTION_INFO_V1(pg_visibility_map_rel);
PG_FUNCTION_INFO_V1(pg_visibility);
@@ -611,6 +625,35 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
}
/*
+ * Callback function to get next block for read stream object used in
+ * collect_corrupt_items() function.
+ */
+static BlockNumber
+collect_corrupt_items_read_stream_next_block(ReadStream *stream,
+
void *callback_private_data,
+
void *per_buffer_data)
+{
+ struct collect_corrupt_items_read_stream_private *p =
callback_private_data;
+
+ for (; p->blocknum < p->nblocks; p->blocknum++)
+ {
+ bool check_frozen = false;
+ bool check_visible = false;
+
+ if (p->all_frozen && VM_ALL_FROZEN(p->rel, p->blocknum,
p->vmbuffer))
+ check_frozen = true;
+ if (p->all_visible && VM_ALL_VISIBLE(p->rel, p->blocknum,
p->vmbuffer))
+ check_visible = true;
+ if (!check_visible && !check_frozen)
+ continue;
+
+ return p->blocknum++;
+ }
+
+ return InvalidBlockNumber;
+}
+
+/*
* Returns a list of items whose visibility map information does not match
* the status of the tuples on the page.
*
@@ -634,6 +677,10 @@ collect_corrupt_items(Oid relid, bool all_visible, bool
all_frozen)
Buffer vmbuffer = InvalidBuffer;
BufferAccessStrategy bstrategy = GetAccessStrategy(BAS_BULKREAD);
TransactionId OldestXmin = InvalidTransactionId;
+ struct collect_corrupt_items_read_stream_private p;
+ ReadStream *stream;
+
+ Assert(all_visible || all_frozen);
rel = relation_open(relid, AccessShareLock);
@@ -658,11 +705,25 @@ collect_corrupt_items(Oid relid, bool all_visible, bool
all_frozen)
items->count = 64;
items->tids = palloc(items->count * sizeof(ItemPointerData));
+ p.blocknum = 0;
+ p.nblocks = nblocks;
+ p.rel = rel;
+ p.vmbuffer = &vmbuffer;
+ p.all_frozen = all_frozen;
+ p.all_visible = all_visible;
+ stream = read_stream_begin_relation(READ_STREAM_FULL,
+
bstrategy,
+
rel,
+
MAIN_FORKNUM,
+
collect_corrupt_items_read_stream_next_block,
+
&p,
+
0);
+
/* Loop over every block in the relation. */
for (blkno = 0; blkno < nblocks; ++blkno)
{
- bool check_frozen = false;
- bool check_visible = false;
+ bool check_frozen = all_frozen;
+ bool check_visible = all_visible;
Buffer buffer;
Page page;
OffsetNumber offnum,
@@ -671,17 +732,20 @@ collect_corrupt_items(Oid relid, bool all_visible, bool
all_frozen)
/* Make sure we are interruptible. */
CHECK_FOR_INTERRUPTS();
- /* Use the visibility map to decide whether to check this page.
*/
- if (all_frozen && VM_ALL_FROZEN(rel, blkno, &vmbuffer))
- check_frozen = true;
- if (all_visible && VM_ALL_VISIBLE(rel, blkno, &vmbuffer))
- check_visible = true;
- if (!check_visible && !check_frozen)
- continue;
-
/* Read and lock the page. */
- buffer = ReadBufferExtended(rel, MAIN_FORKNUM, blkno,
RBM_NORMAL,
-
bstrategy);
+ buffer = read_stream_next_buffer(stream, NULL);
+
+ /*
+ * If the read stream returns an InvalidBuffer, this means all
the
+ * blocks are processed. So, end the stream and loop.
+ */
+ if (buffer == InvalidBuffer)
+ {
+ read_stream_end(stream);
+ stream = NULL;
+ break;
+ }
+
LockBuffer(buffer, BUFFER_LOCK_SHARE);
page = BufferGetPage(buffer);
@@ -778,6 +842,11 @@ collect_corrupt_items(Oid relid, bool all_visible, bool
all_frozen)
UnlockReleaseBuffer(buffer);
}
+ if (stream)
+ {
+ Assert(read_stream_next_buffer(stream, NULL) == InvalidBuffer);
+ read_stream_end(stream);
+ }
/* Clean up. */
if (vmbuffer != InvalidBuffer)
