com.bigdata.journal

Class TestClockSkewDetection

java.lang.Object

junit.framework.Assert

junit.framework.TestCase

junit.framework.TestCase2

com.bigdata.journal.TestClockSkewDetection

All Implemented Interfaces:

junit.framework.Test

public class TestClockSkewDetection
extends TestCase2

Test suite for ClocksNotSynchronizedException. The basic pattern of events is as follows:

 leader   : t1          : timestamp before gather() messages are sent to followers.
 follower :     t2      : timestamp taken when servicing gather() message and sent to leader with response.
 leader   :         t3  : timestamp taken on leader when barrier breaks.
 

Of necessity, these events have a temporal order (t1 BEFORE t2; t2 BEFORE t3). However, there can be skew in the clocks such that the clock on the leader and the clock on the follower(s) are not synchronized. Some clock skew is allowed, but significant clock skew can cause a problem on failover.

The problem arises because the clocks are used to assign timestamps for commit points, and we index into the journal using those timestamps for historical reads (reading on the database as of some wall clock time).

AbstractJournal.commitNow(long) does ensure that time moves forward relative to the timestamp associated with the last commit point on the journal. However, if the skew is large, then this could require waiting for minutes, hours, or days before a new commit time could be assigned.

In order to avoid such long latency during failover, an error is reported proactively if a large clock skew is detected during the release time consensus protocol.

This test suite verifies the logic for detecting clock skew.

Author:

Bryan Thompson

See Also:

Consensus protocol does not detect clock skew correctly

Nested Class Summary

Nested classes/interfaces inherited from class junit.framework.TestCase2

TestCase2.MyProperties, TestCase2.RandomType

Field Summary

Fields inherited from class junit.framework.TestCase2

_randomType, log

Constructor Summary

Constructors

Constructor and Description
TestClockSkewDetection()
TestClockSkewDetection(String name)

Method Summary

Methods

Modifier and Type	Method and Description
protected void	setUp()
protected void	tearDown()
void	test01() Tests where the delta is LT and t1 LT t2
void	test02() Tests where the delta is EQ and t1 LT t2
void	test03() Tests where the delta is GT and t1 LT t2
void	test11() Tests where the delta is LT and t1 GTE t2.
void	test12() Tests where the delta is EQ and t1 GTE t2
void	test13() Tests where the delta is GT and t1 GTE t2

Methods inherited from class junit.framework.TestCase2

assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEqualsWithinUlps, assertSameArray, assertSameArray, assertSameBigDecimal, assertSameBigDecimal, assertSameBigInteger, assertSameBigInteger, assertSameIterator, assertSameIterator, assertSameIteratorAnyOrder, assertSameIteratorAnyOrder, assertSameValue, assertSameValue, assertZeroUlps, assertZeroUlps, fail, getInnerCause, getNormalInt, getProjectBuildPath, getProperties, getRandomObject, getRandomObject, getRandomOrder, getRandomString, getTestInputStream, getTestResource, getTestResource, getUlps, getUlps, isDEBUG, isDEBUG, isINFO, isINFO, isInnerCause, logProperties

Methods inherited from class junit.framework.TestCase

assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertFalse, assertFalse, assertNotNull, assertNotNull, assertNotSame, assertNotSame, assertNull, assertNull, assertSame, assertSame, assertTrue, assertTrue, countTestCases, createResult, fail, fail, failNotEquals, failNotSame, failSame, format, getName, run, run, runBare, runTest, setName, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

TestClockSkewDetection

public TestClockSkewDetection()

TestClockSkewDetection

public TestClockSkewDetection(String name)

Method Detail

setUp

protected void setUp()
              throws Exception

Overrides:

setUp in class junit.framework.TestCase

Throws:

Exception

tearDown

protected void tearDown()
                 throws Exception

Overrides:

tearDown in class junit.framework.TestCase

Throws:

Exception

test01

public void test01()

Tests where the delta is LT and t1 LT t2

test02

public void test02()

Tests where the delta is EQ and t1 LT t2

test03

public void test03()

Tests where the delta is GT and t1 LT t2

test11

public void test11()

Tests where the delta is LT and t1 GTE t2.

Note: This is a test for a "fuzzy" sense of "before". We explicitly allow for some clock skew since it will not cause a significantly latency on failover and minor clock skew (on the order of the latency of an RMI) is common, even with synchronized clocks.

test12

public void test12()

Tests where the delta is EQ and t1 GTE t2

test13

public void test13()

Tests where the delta is GT and t1 GTE t2