com.bigdata.journal

Class TestRandomAccessFileSynchronousWrites

java.lang.Object

junit.framework.Assert

junit.framework.TestCase

com.bigdata.journal.TestRandomAccessFileSynchronousWrites

All Implemented Interfaces:

junit.framework.Test

public class TestRandomAccessFileSynchronousWrites
extends junit.framework.TestCase

Test suite for conformance with synchronous IO write requests made on a RandomAccessFile opened using rss or rdd mode. A conforming platform will NOT reorder writes and will a request to FileChannel.force(boolean) will flush data through to stable media before the write operation returns. A write cache in the operating system, device driver, controller, or disk drive can defeat synchronous IO with the results that: (a) the sequence in which writes are issued by the application may not be the sequence in which the data are laid down on the disk; and (b) the write operation may return before the data are stable on disk.

Both of these results can break the semantics of the atomic commit protocol in at least the following ways:

• If the root blocks are updated before the application data are on stable media then a power failure will cause the application to read from the new root block but the application data will not have been written.
• If the write operation returns before the data are on stable media then the application may conclude that the commit was successful when in fact the data are not yet on disk. In fact, since the error is not reported synchronously the application may never learn that the write has failed unless it continues to write on the disk and a subsequent write turns up the error.

Version:

$Id$

Author:

Bryan Thompson

Field Summary

Fields

Modifier and Type	Field and Description
protected static org.apache.log4j.Logger	log

Constructor Summary

Constructors

Constructor and Description
TestRandomAccessFileSynchronousWrites()
TestRandomAccessFileSynchronousWrites(String name)

Method Summary

Methods

Modifier and Type	Method and Description
protected void	assertWriteCacheDisabled(com.bigdata.journal.TestRandomAccessFileSynchronousWrites.Stats baseline, com.bigdata.journal.TestRandomAccessFileSynchronousWrites.Stats syncio) Verify that the request to sync to disk with each IO (rws or rwd) was honored by the underlying platform.
protected com.bigdata.journal.TestRandomAccessFileSynchronousWrites.Stats	doSyncWriteTest(String mode) Test helper attempts to detect when a request for synchronous writes is being ignored by the platform.
void	test_syncWrites_rdd() Test verifies whether or not the platform appears to perform synchronous IOs when creating a RandomAccessFile with mode rws.
void	test_syncWrites_rds() Test verifies whether or not the platform appears to perform synchronous IOs when creating a RandomAccessFile with mode rws.

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, setUp, tearDown, toString

Methods inherited from class java.lang.Object

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

Field Detail

log

protected static final org.apache.log4j.Logger log

Constructor Detail

TestRandomAccessFileSynchronousWrites

public TestRandomAccessFileSynchronousWrites()

TestRandomAccessFileSynchronousWrites

public TestRandomAccessFileSynchronousWrites(String name)

Method Detail

test_syncWrites_rds

public void test_syncWrites_rds()
                         throws IOException

Test verifies whether or not the platform appears to perform synchronous IOs when creating a RandomAccessFile with mode rws.

Throws:

IOException

test_syncWrites_rdd

public void test_syncWrites_rdd()
                         throws IOException

Test verifies whether or not the platform appears to perform synchronous IOs when creating a RandomAccessFile with mode rws.

Throws:

IOException

assertWriteCacheDisabled

protected void assertWriteCacheDisabled(com.bigdata.journal.TestRandomAccessFileSynchronousWrites.Stats baseline,
                            com.bigdata.journal.TestRandomAccessFileSynchronousWrites.Stats syncio)

Verify that the request to sync to disk with each IO (rws or rwd) was honored by the underlying platform.

Parameters:

baseline - The rw performance Stats.

syncio - The performance for either the rws or rwd modes, which require synchronization to the disk after each write.

Throws:

junit.framework.AssertionFailedError - unless the write IOPs are significantly lower for the syncio condition.

doSyncWriteTest

protected com.bigdata.journal.TestRandomAccessFileSynchronousWrites.Stats doSyncWriteTest(String mode)
                                                                                   throws IOException

Test helper attempts to detect when a request for synchronous writes is being ignored by the platform.

Note: The file is created using the temp file mechanisms so this is only really testing the behavior of the disk on which the temp files are stored.

Note: The more write operations that you request and the larger the file on which those writes are randomly distributed the more you are likely to defeat any cache mechanisms.

    Results on a laptop class platform (Windows XP):
  
  write cache disabled in platform:
  
  elapsed=5063ms, mode=rwd, writesPerSec=988, bytesPerSec=1011258
  elapsed=5031ms, mode=rws, writesPerSec=994, bytesPerSec=1017690
  elapsed=109ms, mode=rw, writesPerSec=45872, bytesPerSec=46972477
  
  write cache enabled in platform:
  
  elapsed=1797ms, mode=rwd, writesPerSec=2782, bytesPerSec=2849193
  elapsed=1969ms, mode=rws, writesPerSec=2539, bytesPerSec=2600305
  elapsed=62ms, mode=rw, writesPerSec=80645, bytesPerSec=82580645
 
 

Based on the data above, you can see that merely requesting synchronous IO in Java clearly does not disable all layers of the write cache.

Parameters:

mode - The file mode to be used.

Returns:

The Stats for that mode.

Throws:

IOException