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PSYNC2: clarify the scenario when repl_stream_db can be -1

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This commit is contained in:
zhaozhao.zz 2017-11-02 10:45:33 +08:00
parent 885c4f856e
commit b8579c225c
2 changed files with 21 additions and 9 deletions
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27
src/rdb.c
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@ -2035,14 +2035,25 @@ rdbSaveInfo *rdbPopulateSaveInfo(rdbSaveInfo *rsi) {
*rsi = rsi_init;
/* If the instance is a master, we can populate the replication info
* in all the cases, even if sometimes in incomplete (but safe) form. */
if (!server.masterhost) {
if (server.repl_backlog) rsi->repl_stream_db = server.slaveseldb;
/* Note that if repl_backlog is NULL, it means that histories
* following from this point will trigger a full synchronization
* generating a SELECT statement, so we can leave the currently
* selected DB set to -1. This allows a restarted master to reload
* its replication ID/offset when there are no connected slaves. */
* only when repl_backlog is not NULL. If the repl_backlog is NULL,
* it means that the instance isn't in any replication chains. In this
* scenario the replication info is useless, because when a slave
* connect to us, the NULL repl_backlog will trigger a full synchronization,
* at the same time we will use a new replid and clear replid2.
* And remember that after free backlog if we reach repl_backlog_time_limit,
* we will use a new replid and clear replid2 too. So there is only one
* scenario which can make repl_stream_db be -1, that is the instance is
* a master, and it have repl_backlog, but server.slaveseldb is -1. */
if (!server.masterhost && server.repl_backlog) {
rsi->repl_stream_db = server.slaveseldb;
/* Note that server.slaveseldb may be -1, it means that this master
* didn't apply any write commands after a full synchronization,
* so we can leave the currently selected DB set to -1, because the
* next write command must generate a SELECT statement. This allows
* a restarted slave to reload replication ID/offset even the repl_stream_db
* is -1, but we should not do that, because older implementations
* may save a repl_stream_db as -1 in a wrong way. Maybe we can fix
* it in the next release version. */
return rsi;
}

3
src/server.c
View File

@ -3536,7 +3536,8 @@ void loadDataFromDisk(void) {
rsi.repl_id_is_set &&
rsi.repl_offset != -1 &&
/* Note that older implementations may save a repl_stream_db
* of -1 inside the RDB file. */
* of -1 inside the RDB file in a wrong way, see more information
* in function rdbPopulateSaveInfo. */
rsi.repl_stream_db != -1)
{
memcpy(server.replid,rsi.repl_id,sizeof(server.replid));