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MXS-1983: Retry message posting

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If the posting of a message to a message queue fails due to the queue
being full, it is retried for a limited number of times. This is a
temporary fix to the problem that fixing MXS-1948 introduced. A proper
solution that leverages SO_REUSEPORT should be implemented in the next
major release.
This commit is contained in:
Markus Mäkelä
2018-07-24 09:45:30 +03:00
parent 1f5e23c674
commit 5b04e492c6
1 changed files with 47 additions and 2 deletions
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49
server/core/messagequeue.cc
View File

@ -175,12 +175,57 @@ bool MessageQueue::post(const Message& message) const
ss_dassert(m_pWorker);
if (m_pWorker)
{
ssize_t n = write(m_write_fd, &message, sizeof(message));
rv = (n == sizeof(message));
/**
* This is a stopgap measure to solve MXS-1983 that causes Resource temporarily
* unavailable errors. The errors are caused by the pipe buffer being too small to
* hold all worker messages. By retrying a limited number of times before giving
* up, the success rate for posted messages under heavy load increases
* significantly.
*/
int fast = 0;
int slow = 0;
const int fast_size = 100;
const int slow_limit = 3;
ssize_t n;
while (true)
{
n = write(m_write_fd, &message, sizeof(message));
rv = (n == sizeof(message));
if (n == -1 && (errno == EAGAIN || errno == EWOULDBLOCK))
{
if (++fast > fast_size)
{
fast = 0;
if (++slow >= slow_limit)
{
break;
}
else
{
sched_yield()
}
}
}
else
{
break;
}
}
if (n == -1)
{
MXS_ERROR("Failed to write message: %d, %s", errno, mxs_strerror(errno));
static bool warn_pipe_buffer_size = true;
if ((errno == EAGAIN || errno == EWOULDBLOCK) && warn_pipe_buffer_size)
{
MXS_ERROR("Consider increasing pipe buffer size (sysctl fs.pipe-max-size)");
warn_pipe_buffer_size = false;
}
}
}
else