Re: Race conditions, race conditions!

"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes
>
> WARNING: relation "t1" page 196 is uninitialized --- fixing
> TRAP: FailedAssertion("!((((PageHeader) ((PageHeader)
pageHeader))->pd_upper == 0))", File: "hio.c", Line: 263)
> LOG: server process (PID 11296) was terminated by signal 6
>

Inspired by this, can we put an asseration here:

---
/*
* lookup the buffer. IO_IN_PROGRESS is set if the requested
* block is not currently in memory.
*/
bufHdr = BufferAlloc(reln, blockNum, &found);

+ /* we are guaranted that nobody else has touched this will-be-new block */
+ Assert(!(found && isExtend));

if (found)
BufferHitCount++;
---

BufferAlloc() consists of two parts, one is looking for the blockNum, the
other is allocating a free buffer. If the asseration is good, then for
"isExtend", we just need the second part. This could bring marginal
performance benefits.

Regards,
Qingqing