Hi Melih, > I would appreciate any feedback/comment on this change.
Another benefit of pg_buffercache_summary() you didn't mention is that
it allocates much less memory than pg_buffercache_pages() does.
Here is v3 where I added this to the documentation. The patch didn't
apply to the current master branch with the following error:
```
pg_buffercache_pages.c:286:19: error: no member named 'rlocator' in
'struct buftag'
if (bufHdr->tag.rlocator.relNumber != InvalidOid)
~~~~~~~~~~~ ^
1 error generated.
```
I fixed this too. Additionally, the patch was pgindent'ed and some
typos were fixed.
However I'm afraid you can't examine BufferDesc's without taking
locks. This is explicitly stated in buf_internals.h:
"""
Buffer header lock (BM_LOCKED flag) must be held to EXAMINE or change
TAG, state or wait_backend_pgprocno fields.
"""
Let's consider this code again (this is after my fix):
```
if (RelFileNumberIsValid(BufTagGetRelNumber(bufHdr))) {
/* ... */
}
```
When somebody modifies relNumber concurrently (e.g. calls
ClearBufferTag()) this will cause an undefined behaviour.
I suggest we focus on saving the memory first and then think about the
performance, if necessary.
--
Best regards,
Aleksander Alekseev
v3-0001-Added-pg_buffercache_summary-function.patch
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