Re: "cache reference leak" and "problem in alloc set" warnings

Volkan YAZICI <yazicivo(at)ttnet(dot)net(dot)tr> writes:
> I've still biten by a single "write past chunk" error while returning a
> record in PL/scheme:

> WARNING: problem in alloc set ExprContext: detected write past chunk
> end in block 0x84a0598, chunk 0x84a0c84

The actual bug, almost certainly, is that you're miscomputing the space
needed for a variable-size palloc request. But tracking that down will
be hard until you find out which chunk it is.

Do you have a sequence that will make the problem happen consistently at
the same address? If so, you can use a gdb watchpoint to find out where
the write-past-end is happening. Or use a conditional breakpoint in
AllocSetAlloc to try to identify where the chunk is handed out.

Another possibility is to set a breakpoint where the warning is emitted
and take a look at the contents of the chunk to see if you can identify
it; that wouldn't require knowing the target chunk address in advance.

BTW, if I recall that code correctly, the "chunk address" in the message
is probably the address of the start of the overhead data for the chunk,
not the usable-space start address that is passed back by palloc.

regards, tom lane