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Use replicationFeedSlaves() to send PING to slaves.

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A Redis master sends PING commands to slaves from time to time: doing
this ensures that even if absence of writes, the master->slave channel
remains active and the slave can feel the master presence, instead of
closing the connection for timeout.

This commit changes the way PINGs are sent to slaves in order to use the
standard interface used to replicate all the other commands, that is,
the function replicationFeedSlaves().

With this change the stream of commands sent to every slave is exactly
the same regardless of their exact state (Transferring RDB for first
synchronization or slave already online). With the previous
implementation the PING was only sent to online slaves, with the result
that the output stream from master to slaves was not identical for all
the slaves: this is a problem if we want to implement partial resyncs in
the future using a global replication stream offset.

TL;DR: this commit should not change the behaviour in practical terms,
but is just something in preparation for partial resynchronization
support.
This commit is contained in:
antirez 2012-11-03 11:56:28 +01:00
parent 7465ac7ab1
commit 4b83ad4e1f
2 changed files with 22 additions and 22 deletions
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20
src/redis.h
View File

@ -197,7 +197,7 @@
#define REDIS_CLIENT_LIMIT_CLASS_PUBSUB 2
#define REDIS_CLIENT_LIMIT_NUM_CLASSES 3
/* Slave replication state - slave side */
/* Slave replication state - from the point of view of the slave. */
#define REDIS_REPL_NONE 0 /* No active replication */
#define REDIS_REPL_CONNECT 1 /* Must connect to master */
#define REDIS_REPL_CONNECTING 2 /* Connecting to master */
@ -205,17 +205,17 @@
#define REDIS_REPL_TRANSFER 4 /* Receiving .rdb from master */
#define REDIS_REPL_CONNECTED 5 /* Connected to master */
/* Synchronous read timeout - slave side */
#define REDIS_REPL_SYNCIO_TIMEOUT 5
/* Slave replication state - from the point of view of master
* Note that in SEND_BULK and ONLINE state the slave receives new updates
/* Slave replication state - from the point of view of the master.
* In SEND_BULK and ONLINE state the slave receives new updates
* in its output queue. In the WAIT_BGSAVE state instead the server is waiting
* to start the next background saving in order to send updates to it. */
#define REDIS_REPL_WAIT_BGSAVE_START 3 /* master waits bgsave to start feeding it */
#define REDIS_REPL_WAIT_BGSAVE_END 4 /* master waits bgsave to start bulk DB transmission */
#define REDIS_REPL_SEND_BULK 5 /* master is sending the bulk DB */
#define REDIS_REPL_ONLINE 6 /* bulk DB already transmitted, receive updates */
#define REDIS_REPL_WAIT_BGSAVE_START 6 /* We need to produce a new RDB file. */
#define REDIS_REPL_WAIT_BGSAVE_END 7 /* Waiting RDB file creation to finish. */
#define REDIS_REPL_SEND_BULK 8 /* Sending RDB file to slave. */
#define REDIS_REPL_ONLINE 9 /* RDB file transmitted, sending just updates. */
/* Synchronous read timeout - slave side */
#define REDIS_REPL_SYNCIO_TIMEOUT 5
/* List related stuff */
#define REDIS_HEAD 0

24
src/replication.c
View File

@ -803,23 +803,23 @@ void replicationCron(void) {
if (!(server.cronloops % (server.repl_ping_slave_period * server.hz))) {
listIter li;
listNode *ln;
robj *ping_argv[1];
/* First, send PING */
ping_argv[0] = createStringObject("PING",4);
replicationFeedSlaves(server.slaves, server.slaveseldb, ping_argv, 1);
decrRefCount(ping_argv[0]);
/* Second, send a newline to all the slaves in pre-synchronization stage,
* that is, slaves waiting for the master to create the RDB file.
* The newline will be ignored by the slave but will refresh the
* last-io timer preventing a timeout. */
listRewind(server.slaves,&li);
while((ln = listNext(&li))) {
redisClient *slave = ln->value;
/* Don't ping slaves that are in the middle of a bulk transfer
* with the master for first synchronization. */
if (slave->replstate == REDIS_REPL_SEND_BULK) continue;
if (slave->replstate == REDIS_REPL_ONLINE) {
/* If the slave is online send a normal ping */
addReplySds(slave,sdsnew("*1\r\n$4\r\nPING\r\n"));
} else {
/* Otherwise we are in the pre-synchronization stage.
* Just a newline will do the work of refreshing the
* connection last interaction time, and at the same time
* we'll be sure that being a single char there are no
* short-write problems. */
if (slave->replstate == REDIS_REPL_WAIT_BGSAVE_START ||
slave->replstate == REDIS_REPL_WAIT_BGSAVE_END) {
if (write(slave->fd, "\n", 1) == -1) {
/* Don't worry, it's just a ping. */
}