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https://issues.apache.org/jira/browse/HIVE-15077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16374883#comment-16374883
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Alan Gates commented on HIVE-15077:
-----------------------------------
+1. The previous code was trying to save time by only comparing against some
of the locks, but since the sort or was changed in HIVE-10242 that no longer
works.
> Acid LockManager is unfair
> --------------------------
>
> Key: HIVE-15077
> URL: https://issues.apache.org/jira/browse/HIVE-15077
> Project: Hive
> Issue Type: Bug
> Components: Transactions
> Affects Versions: 2.3.0
> Reporter: Eugene Koifman
> Assignee: Eugene Koifman
> Priority: Blocker
> Attachments: HIVE-15077.02.patch
>
>
> HIVE-10242 made the acid LM unfair.
> In TxnHandler.checkLock(), suppose we are trying to acquire SR5 (the number
> is extLockId).
> Then
> LockInfo[] locks = lockSet.toArray(new LockInfo[lockSet.size()]);
> may look like this (all explicitly listed locks are in Waiting state)
> {...., SR5 SW3 X4}
> So the algorithm will find SR5 in the list and start looking backwards (to
> the left).
> According to IDs, SR5 should wait for X4 to be granted but X4 won't even be
> examined and so SR5 may be granted.
> Theoretically, this could cause starvation.
> The query that generates the list already has
> query.append(" and hl_lock_ext_id <= ").append(extLockId);
> but it should use "<" rather than "<=" to exclude the locks being checked
> from "locks" list which will make the algorithm look at all locks "in front"
> of a given lock.
> Here is an example (add to TestDbTxnManager2)
> {noformat}
> @Test
> public void testFairness2() throws Exception {
> dropTable(new String[]{"T7"});
> CommandProcessorResponse cpr = driver.run("create table if not exists T7
> (a int) partitioned by (p int) stored as orc TBLPROPERTIES
> ('transactional'='true')");
> checkCmdOnDriver(cpr);
> checkCmdOnDriver(driver.run("insert into T7 partition(p)
> values(1,1),(1,2)"));//create 2 partitions
> cpr = driver.compileAndRespond("select a from T7 ");
> checkCmdOnDriver(cpr);
> txnMgr.acquireLocks(driver.getPlan(), ctx, "Fifer");//gets S lock on T7
> HiveTxnManager txnMgr2 =
> TxnManagerFactory.getTxnManagerFactory().getTxnManager(conf);
> swapTxnManager(txnMgr2);
> cpr = driver.compileAndRespond("alter table T7 drop partition (p=1)");
> checkCmdOnDriver(cpr);
> //tries to get X lock on T7.p=1 and gets Waiting state
> LockState lockState = ((DbTxnManager)
> txnMgr2).acquireLocks(driver.getPlan(), ctx, "Fiddler", false);
> List<ShowLocksResponseElement> locks = getLocks();
> Assert.assertEquals("Unexpected lock count", 4, locks.size());
> checkLock(LockType.SHARED_READ, LockState.ACQUIRED, "default", "T7",
> null, locks);
> checkLock(LockType.SHARED_READ, LockState.ACQUIRED, "default", "T7",
> "p=1", locks);
> checkLock(LockType.SHARED_READ, LockState.ACQUIRED, "default", "T7",
> "p=2", locks);
> checkLock(LockType.EXCLUSIVE, LockState.WAITING, "default", "T7", "p=1",
> locks);
> HiveTxnManager txnMgr3 =
> TxnManagerFactory.getTxnManagerFactory().getTxnManager(conf);
> swapTxnManager(txnMgr3);
> //this should block behind the X lock on T7.p=1
> cpr = driver.compileAndRespond("select a from T7");
> checkCmdOnDriver(cpr);
> txnMgr3.acquireLocks(driver.getPlan(), ctx, "Fifer");//gets S lock on T6
> locks = getLocks();
> Assert.assertEquals("Unexpected lock count", 7, locks.size());
> checkLock(LockType.SHARED_READ, LockState.ACQUIRED, "default", "T7",
> null, locks);
> checkLock(LockType.SHARED_READ, LockState.ACQUIRED, "default", "T7",
> "p=1", locks);
> checkLock(LockType.SHARED_READ, LockState.ACQUIRED, "default", "T7",
> "p=2", locks);
> checkLock(LockType.SHARED_READ, LockState.ACQUIRED, "default", "T7",
> null, locks);
> checkLock(LockType.SHARED_READ, LockState.ACQUIRED, "default", "T7",
> "p=1", locks);
> checkLock(LockType.SHARED_READ, LockState.ACQUIRED, "default", "T7",
> "p=2", locks);
> checkLock(LockType.EXCLUSIVE, LockState.WAITING, "default", "T7", "p=1",
> locks);
> }
> {noformat}
> The 2nd {{locks = getLocks();}} output shows that all locks for the 2nd
> {{select * from T7}} are all acquired while they should block behind the X
> lock to be fair.
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