ashutosh-bapat commented on a change in pull request #684: HIVE-21880 : Enable
flaky test
TestReplicationScenariosAcidTablesBootstrap.testBootstrapAcidTablesDuringIncrementalWithConcurrentWrites.
URL: https://github.com/apache/hive/pull/684#discussion_r299064763
##########
File path:
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/ObjectStore.java
##########
@@ -10000,17 +10000,25 @@ private void prepareQuotes() throws SQLException {
}
}
- private void lockForUpdate() throws MetaException {
- String selectQuery = "select \"NEXT_EVENT_ID\" from
\"NOTIFICATION_SEQUENCE\"";
- String selectForUpdateQuery = sqlGenerator.addForUpdateClause(selectQuery);
- new RetryingExecutor(conf, () -> {
- prepareQuotes();
- Query query = pm.newQuery("javax.jdo.query.SQL", selectForUpdateQuery);
- query.setUnique(true);
- // only need to execute it to get db Lock
- query.execute();
- query.closeAll();
- }).run();
+ private void lockNotificationSequenceForUpdate() throws MetaException {
+ if (sqlGenerator.getDbProduct() == DatabaseProduct.DERBY && directSql !=
null) {
+ // Derby doesn't allow FOR UPDATE to lock the row being selected (See
https://db.apache
+ // .org/derby/docs/10.1/ref/rrefsqlj31783.html) . So lock the whole
table. Since there's
+ // only one row in the table, this shouldn't cause any performance
degradation. Also we not
+ // suggest Derby to be used in production so that's fine.
+ directSql.lockDbTable("NOTIFICATION_SEQUENCE");
Review comment:
LOCK table is more restrictive than SELECT FOR UPDATE. E.g. LOCK table in
exclusive mode will block any SELECTs as well, but SELECT FOR UPDATE will allow
SELECT. So, it's better to restrict this method only to Derby where SELECT FOR
UPDATE is not possible.
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