From 5f716ea467d29059a89f90b6ccbdee5a60443200 Mon Sep 17 00:00:00 2001
From: Luke Palmer <luke@lukepalmer.net>
Date: Wed, 15 Jul 2020 13:53:41 -0400
Subject: Send null for invalidate on flush (#7469)

---
 src/tracking.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

(limited to 'src/tracking.c')

diff --git a/src/tracking.c b/src/tracking.c
index 8c2dca7ba..2721de32a 100644
--- a/src/tracking.c
+++ b/src/tracking.c
@@ -198,9 +198,11 @@ void trackingRememberKeys(client *c) {
  *
  * In case the 'proto' argument is non zero, the function will assume that
  * 'keyname' points to a buffer of 'keylen' bytes already expressed in the
- * form of Redis RESP protocol, representing an array of keys to send
- * to the client as value of the invalidation. This is used in BCAST mode
- * in order to optimized the implementation to use less CPU time. */
+ * form of Redis RESP protocol. This is used for:
+ * - In BCAST mode, to send an array of invalidated keys to all
+ *   applicable clients
+ * - Following a flush command, to send a single RESP NULL to indicate
+ *   that all keys are now invalid. */
 void sendTrackingMessage(client *c, char *keyname, size_t keylen, int proto) {
     int using_redirection = 0;
     if (c->client_tracking_redirection) {
@@ -342,17 +344,19 @@ void trackingInvalidateKey(client *c, robj *keyobj) {
     trackingInvalidateKeyRaw(c,keyobj->ptr,sdslen(keyobj->ptr),1);
 }
 
-/* This function is called when one or all the Redis databases are flushed
- * (dbid == -1 in case of FLUSHALL). Caching keys are not specific for
- * each DB but are global: currently what we do is send a special
- * notification to clients with tracking enabled, invalidating the caching
- * key "", which means, "all the keys", in order to avoid flooding clients
- * with many invalidation messages for all the keys they may hold.
+/* This function is called when one or all the Redis databases are
+ * flushed (dbid == -1 in case of FLUSHALL). Caching keys are not
+ * specific for each DB but are global: currently what we do is send a
+ * special notification to clients with tracking enabled, sending a
+ * RESP NULL, which means, "all the keys", in order to avoid flooding
+ * clients with many invalidation messages for all the keys they may
+ * hold.
  */
 void freeTrackingRadixTree(void *rt) {
     raxFree(rt);
 }
 
+/* A RESP NULL is sent to indicate that all keys are invalid */
 void trackingInvalidateKeysOnFlush(int dbid) {
     if (server.tracking_clients) {
         listNode *ln;
@@ -361,7 +365,7 @@ void trackingInvalidateKeysOnFlush(int dbid) {
         while ((ln = listNext(&li)) != NULL) {
             client *c = listNodeValue(ln);
             if (c->flags & CLIENT_TRACKING) {
-                sendTrackingMessage(c,"",1,0);
+                sendTrackingMessage(c,shared.null[c->resp]->ptr,sdslen(shared.null[c->resp]->ptr),1);
             }
         }
     }
-- 
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