postgres.git / summary / log / commit / refs

commit    d212957254de85aad934e2601e5a07661db268fb
Author:   Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date:     Fri Feb 02 19:12:30 2024 +0000
First released in: 17.0

    Fix bug in bulk extending temp relation after failure
    
    A ResourceOwnerEnlarge() call was missing. That led to an error:
    
    ERROR:  ResourceOwnerRemember called but array was full
    
    and an assertion failure, if you tried to extend a temp relation again
    after a failure. Alexander's test case used running out of disk space
    to trigger the original failure.
    
    This bug was introduced in the large ResourceOwner rewrite commit
    b8bff07daa. Before that, the UnpinLocalBuffer() call guaranteed that
    the subsequent PinLocalBuffer() will succeed, but after the rewrite,
    releasing an old resource doesn't guarantee that there is space for a
    new one.
    
    Add a comment explaining why the UnpinBuffer + PinBuffer calls in
    BufferAlloc(), with no ResourceOwnerEnlarge() in between, are safe.
    
    Reported-by: Alexander Lakhin
    Discussion: https://www.postgresql.org/message-id/dc574fea-c83e-a600-08cd-10881762e4fa@gmail.com


 src/backend/storage/buffer/localbuf.c | 5 +++++
 src/backend/utils/resowner/resowner.c | 7 ++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c
index 1be4f4f8daf..1f02fed250e 100644
--- a/src/backend/storage/buffer/localbuf.c
+++ b/src/backend/storage/buffer/localbuf.c
@@ -374,6 +374,9 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
 		victim_buf_id = -buffers[i] - 1;
 		victim_buf_hdr = GetLocalBufferDescriptor(victim_buf_id);
 
+		/* in case we need to pin an existing buffer below */
+		ResourceOwnerEnlarge(CurrentResourceOwner);
+
 		InitBufferTag(&tag, &bmr.smgr->smgr_rlocator.locator, fork, first_block + i);
 
 		hresult = (LocalBufferLookupEnt *)
@@ -646,6 +649,8 @@ InitLocalBuffers(void)
  * XXX: We could have a slightly more efficient version of PinLocalBuffer()
  * that does not support adjusting the usagecount - but so far it does not
  * seem worth the trouble.
+ *
+ * Note that ResourceOwnerEnlarge() must have been done already.
  */
 bool
 PinLocalBuffer(BufferDesc *buf_hdr, bool adjust_usagecount)
diff --git a/src/backend/utils/resowner/resowner.c b/src/backend/utils/resowner/resowner.c
index 67cc332e80d..aa199b23ffd 100644
--- a/src/backend/utils/resowner/resowner.c
+++ b/src/backend/utils/resowner/resowner.c
@@ -548,8 +548,13 @@ ResourceOwnerRemember(ResourceOwner owner, Datum value, const ResourceOwnerDesc
 /*
  * Forget that an object is owned by a ResourceOwner
  *
- * Note: if same resource ID is associated with the ResourceOwner more than
+ * Note: If same resource ID is associated with the ResourceOwner more than
  * once, one instance is removed.
+ *
+ * Note: Forgetting a resource does not guarantee that there is room to
+ * remember a new resource.  One exception is when you forget the most
+ * recently remembered resource; that does make room for a new remember call.
+ * Some code callers rely on that exception.
  */
 void
 ResourceOwnerForget(ResourceOwner owner, Datum value, const ResourceOwnerDesc *kind)


[parent: 7e0ade0ffe0a]