From cd8de095c4dc6687dabaa194a0fff4473c52299f Mon Sep 17 00:00:00 2001
From: kronwerk <kronwerk@users.noreply.github.com>
Date: Wed, 9 Oct 2024 14:11:53 +0300
Subject: [PATCH] Add flush-before-load option for repl-diskless-load (#909)
A new option for diskless replication on the replica side.
After a network failure, the replica may need to perform a full sync.
The other option for diskless full sync is `swapdb`, but it uses twice
as much memory, temporarily. In situations where this is not acceptable,
and where losing data is acceptable, the `flush-before-load` can be
useful. If the full sync fails, the old data is lost though. Therefore,
the new option is marked as "dangerous".
---------
Signed-off-by: kronwerk <ca11e5e22g@gmail.com>
Signed-off-by: kronwerk <kronwerk@users.noreply.github.com>
Co-authored-by: kronwerk <ca11e5e22g@gmail.com>
---
src/config.c | 1 +
src/replication.c | 1 +
src/server.h | 1 +
tests/integration/replication.tcl | 57 +++++++++++++++++++++++++++++++
valkey.conf | 25 ++++++++------
5 files changed, 74 insertions(+), 11 deletions(-)
diff --git a/src/config.c b/src/config.c
index 6c03cbb47..62ed5dd91 100644
--- a/src/config.c
+++ b/src/config.c
@@ -107,6 +107,7 @@ configEnum repl_diskless_load_enum[] = {
{"disabled", REPL_DISKLESS_LOAD_DISABLED},
{"on-empty-db", REPL_DISKLESS_LOAD_WHEN_DB_EMPTY},
{"swapdb", REPL_DISKLESS_LOAD_SWAPDB},
+ {"flush-before-load", REPL_DISKLESS_LOAD_FLUSH_BEFORE_LOAD},
{NULL, 0}};
configEnum tls_auth_clients_enum[] = {
diff --git a/src/replication.c b/src/replication.c
index 64df85f19..e2941c6d9 100644
--- a/src/replication.c
+++ b/src/replication.c
@@ -1943,6 +1943,7 @@ void restartAOFAfterSYNC(void) {
static int useDisklessLoad(void) {
/* compute boolean decision to use diskless load */
int enabled = server.repl_diskless_load == REPL_DISKLESS_LOAD_SWAPDB ||
+ server.repl_diskless_load == REPL_DISKLESS_LOAD_FLUSH_BEFORE_LOAD ||
(server.repl_diskless_load == REPL_DISKLESS_LOAD_WHEN_DB_EMPTY && dbTotalServerKeyCount() == 0);
if (enabled) {
diff --git a/src/server.h b/src/server.h
index 84a282b6f..84ce96a49 100644
--- a/src/server.h
+++ b/src/server.h
@@ -490,6 +490,7 @@ typedef enum {
#define REPL_DISKLESS_LOAD_DISABLED 0
#define REPL_DISKLESS_LOAD_WHEN_DB_EMPTY 1
#define REPL_DISKLESS_LOAD_SWAPDB 2
+#define REPL_DISKLESS_LOAD_FLUSH_BEFORE_LOAD 3
/* TLS Client Authentication */
#define TLS_CLIENT_AUTH_NO 0
diff --git a/tests/integration/replication.tcl b/tests/integration/replication.tcl
index 203574e39..1b5b0c030 100644
--- a/tests/integration/replication.tcl
+++ b/tests/integration/replication.tcl
@@ -1478,6 +1478,63 @@ start_server {tags {"repl external:skip"}} {
}
}
+foreach dualchannel {yes no} {
+ test "replica actually flushes db if use diskless load with flush-before-load dual-channel-replication-enabled=$dualchannel" {
+ start_server {tags {"repl"}} {
+ set replica [srv 0 client]
+ set replica_log [srv 0 stdout]
+ start_server {} {
+ set master [srv 0 client]
+ set master_host [srv 0 host]
+ set master_port [srv 0 port]
+
+ # Fill both replica and master with data
+ $master debug populate 100 master 100000
+ $replica debug populate 201 replica 100000
+ assert_equal [$replica dbsize] 201
+ # Set up master
+ $master config set save ""
+ $master config set rdbcompression no
+ $master config set repl-diskless-sync yes
+ $master config set repl-diskless-sync-delay 0
+ $master config set dual-channel-replication-enabled $dualchannel
+ # Set master with a slow rdb generation, so that we can easily intercept loading
+ # 10ms per key, with 1000 keys is 10 seconds
+ $master config set rdb-key-save-delay 10000
+ # Set up replica
+ $replica config set save ""
+ $replica config set repl-diskless-load flush-before-load
+ $replica config set dual-channel-replication-enabled $dualchannel
+ # Start the replication process...
+ $replica replicaof $master_host $master_port
+
+ wait_for_condition 100 100 {
+ [s -1 loading] eq 1
+ } else {
+ fail "Replica didn't start loading"
+ }
+
+ # Make sure that next sync will not start immediately so that we can catch the replica in between syncs
+ $master config set repl-diskless-sync-delay 5
+
+ # Kill the replica connection on the master
+ set killed [$master client kill type replica]
+
+ wait_for_condition 100 100 {
+ [s -1 loading] eq 0
+ } else {
+ fail "Replica didn't disconnect"
+ }
+
+ assert_equal [$replica dbsize] 0
+
+ # Speed up shutdown
+ $master config set rdb-key-save-delay 0
+ }
+ }
+ } {} {external:skip}
+}
+
start_server {tags {"repl external:skip"}} {
set replica [srv 0 client]
$replica set replica_key replica_value
diff --git a/valkey.conf b/valkey.conf
index 56110a52b..9793d7825 100644
--- a/valkey.conf
+++ b/valkey.conf
@@ -667,17 +667,20 @@ repl-diskless-sync-max-replicas 0
# fully loaded in memory, resulting in higher memory usage.
# For this reason we have the following options:
#
-# "disabled" - Don't use diskless load (store the rdb file to the disk first)
-# "swapdb" - Keep current db contents in RAM while parsing the data directly
-# from the socket. Replicas in this mode can keep serving current
-# dataset while replication is in progress, except for cases where
-# they can't recognize primary as having a data set from same
-# replication history.
-# Note that this requires sufficient memory, if you don't have it,
-# you risk an OOM kill.
-# "on-empty-db" - Use diskless load only when current dataset is empty. This is
-# safer and avoid having old and new dataset loaded side by side
-# during replication.
+# "disabled" - Don't use diskless load (store the rdb file to the disk first)
+# "swapdb" - Keep current db contents in RAM while parsing the data directly
+# from the socket. Replicas in this mode can keep serving current
+# dataset while replication is in progress, except for cases where
+# they can't recognize primary as having a data set from same
+# replication history.
+# Note that this requires sufficient memory, if you don't have it,
+# you risk an OOM kill.
+# "on-empty-db" - Use diskless load only when current dataset is empty. This is
+# safer and avoid having old and new dataset loaded side by side
+# during replication.
+# "flush-before-load" - [dangerous] Flush all data before parsing. Note that if
+# there's a problem before the replication succeeded you may
+# lose all your data.
repl-diskless-load disabled
# This dual channel replication sync feature optimizes the full synchronization process