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shm_mq: Update mq_bytes_written less often.

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Do not update shm_mq's mq_bytes_written until we have written
an amount of data greater than 1/4th of the ring size, unless
the caller of shm_mq_send(v) requests a flush at the end of
the message. This reduces the number of calls to SetLatch(),
and also the number of CPU cache misses, considerably, and thus
makes shm_mq significantly faster.

Dilip Kumar, reviewed by Zhihong Yu and Tomas Vondra. Some
minor cosmetic changes by me.

Discussion: http://postgr.es/m/CAFiTN-tVXqn_OG7tHNeSkBbN+iiCZTiQ83uakax43y1sQb2OBA@mail.gmail.com
This commit is contained in:
Robert Haas
2021-10-14 16:06:43 -04:00
parent 7821a0bf20
commit 46846433a0
6 changed files with 69 additions and 19 deletions
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8
src/include/storage/shm_mq.h
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@@ -70,11 +70,13 @@ extern shm_mq *shm_mq_get_queue(shm_mq_handle *mqh);
/* Send or receive messages. */
extern shm_mq_result shm_mq_send(shm_mq_handle *mqh,
Size nbytes, const void *data, bool nowait);
extern shm_mq_result shm_mq_sendv(shm_mq_handle *mqh,
shm_mq_iovec *iov, int iovcnt, bool nowait);
Size nbytes, const void *data, bool nowait,
bool force_flush);
extern shm_mq_result shm_mq_sendv(shm_mq_handle *mqh, shm_mq_iovec *iov,
int iovcnt, bool nowait, bool force_flush);
extern shm_mq_result shm_mq_receive(shm_mq_handle *mqh,
Size *nbytesp, void **datap, bool nowait);
extern void shm_mq_flush(shm_mq_handle *mqh);
/* Wait for our counterparty to attach to the queue. */
extern shm_mq_result shm_mq_wait_for_attach(shm_mq_handle *mqh);