hanm commented on a change in pull request #1069: ZOOKEEPER-3056: Fails to load
database with missing snapshot file but with valid transaction log file.
URL: https://github.com/apache/zookeeper/pull/1069#discussion_r319677093
##########
File path:
zookeeper-server/src/main/java/org/apache/zookeeper/server/persistence/FileTxnSnapLog.java
##########
@@ -232,11 +240,19 @@ public long restore(DataTree dt, Map<Long, Integer>
sessions, PlayBackListener l
} else {
trustEmptyDB = autoCreateDB;
}
+
if (-1L == deserializeResult) {
/* this means that we couldn't find any snapshot, so we need to
* initialize an empty database (reported in ZOOKEEPER-2325) */
if (txnLog.getLastLoggedZxid() != -1) {
- throw new IOException("No snapshot found, but there are log
entries. " + "Something is broken!");
+ // ZOOKEEPER-3056: provides an escape hatch for users upgrading
+ // from old versions of zookeeper (3.4.x, pre 3.5.3).
+ if (!trustEmptySnapshot) {
+ throw new IOException(EMPTY_SNAPSHOT_WARNING + "Something
is broken!");
+ } else {
+ LOG.warn(EMPTY_SNAPSHOT_WARNING + "This should only be
allowed during upgrading.");
+ trustEmptySnapshot = false;
+ }
}
if (trustEmptyDB) {
Review comment:
I thought about this, and I didn't get into `trustEmptyDB` because it seems
create another problem for upgrading, which might require a separate discussion.
Basically if we don't set `trustEmptyDB`, then it's possible to have
zookeeper server in a valid state with no snapshot files but only transaction
log files similar to older version of ZooKeeper. Since we treat such case as
invalid, yet we essentially allow such case happen in first place, this seems
self contradictory and inconsistent. Always creating at least one snapshot
sounds like a good solution here, but that require we always execute the code
path when `trustEmptyDB ` is set (which, is the default case).
Is there any cases where we don't want to set `trustEmptyDB ` ?
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