[ https://issues.apache.org/jira/browse/HIVE-15077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16366255#comment-16366255 ]
Eugene Koifman commented on HIVE-15077: --------------------------------------- no related failures [~alangates] could you review please > 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. -- This message was sent by Atlassian JIRA (v7.6.3#76005)