calculation for NUM_FIXED_LWLOCKS
| От | Amit Kapila |
|---|---|
| Тема | calculation for NUM_FIXED_LWLOCKS |
| Дата | |
| Msg-id | CAA4eK1JQrxZ15GgsHUFe1Yx7k5-9+k9qqDR=rVkM1DOfKox1pw@mail.gmail.com обсуждение исходный текст |
| Ответы |
Re: calculation for NUM_FIXED_LWLOCKS
|
| Список | pgsql-hackers |
Currently the calculation for NUM_FIXED_LWLOCKS is as
below, which I think has some problem:
/* Offsets for various chunks of preallocated lwlocks. */
#define BUFFER_MAPPING_LWLOCK_OFFSET NUM_INDIVIDUAL_LWLOCKS
#define LOCK_MANAGER_LWLOCK_OFFSET \
(BUFFER_MAPPING_LWLOCK_OFFSET + NUM_BUFFER_PARTITIONS)
#define PREDICATELOCK_MANAGER_LWLOCK_OFFSET \
(NUM_INDIVIDUAL_LWLOCKS + NUM_LOCK_PARTITIONS)
#define NUM_FIXED_LWLOCKS \
(PREDICATELOCK_MANAGER_LWLOCK_OFFSET + NUM_PREDICATELOCK_PARTITIONS)
In this PREDICATELOCK_MANAGER_LWLOCK_OFFSET
should consider NUM_BUFFER_PARTITIONS which means
it should be:
#define PREDICATELOCK_MANAGER_LWLOCK_OFFSET \
(LOCK_MANAGER_LWLOCK_OFFSET + NUM_LOCK_PARTITIONS)
If we don't consider buffer partitions in above calculation,
then the total shared memory allocated for fixed locks will
be wrong and can cause problems.
I have noticed this during my work on scaling shared
buffers where if I increase NUM_BUFFER_PARTITIONS,
it leads to hang for tpc-b test and as per my analysis
the reason is above calculation.
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