From 4ff47a0b9bf4d032891e1956c74a5556e443b7a0 Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Fri, 20 Jul 2018 09:46:18 +0200
Subject: [PATCH] Top comment clientsCron().
---
src/server.c | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)
diff --git a/src/server.c b/src/server.c
index 1cb7a9e8e..93c0a46fd 100644
--- a/src/server.c
+++ b/src/server.c
@@ -940,12 +940,27 @@ void getExpansiveClientsInfo(size_t *in_usage, size_t *out_usage) {
*out_usage = o;
}
+/* This function is called by serverCron() and is used in order to perform
+ * operations on clients that are important to perform constantly. For instance
+ * we use this function in order to disconnect clients after a timeout, including
+ * clients blocked in some blocking command with a non-zero timeout.
+ *
+ * The function makes some effort to process all the clients every second, even
+ * if this cannot be strictly guaranteed, since serverCron() may be called with
+ * an actual frequency lower than server.hz in case of latency events like slow
+ * commands.
+ *
+ * It is very important for this function, and the functions it calls, to be
+ * very fast: sometimes Redis has tens of hundreds of connected clients, and the
+ * default server.hz value is 10, so sometimes here we need to process thousands
+ * of clients per second, turning this function into a source of latency.
+ */
#define CLIENTS_CRON_MIN_ITERATIONS 5
void clientsCron(void) {
- /* Make sure to process at least numclients/server.hz of clients
- * per call. Since this function is called server.hz times per second
- * we are sure that in the worst case we process all the clients in 1
- * second. */
+ /* Try to process at least numclients/server.hz of clients
+ * per call. Since normally (if there are no big latency events) this
+ * function is called server.hz times per second, in the average case we
+ * process all the clients in 1 second. */
int numclients = listLength(server.clients);
int iterations = numclients/server.hz;
mstime_t now = mstime();