Hi Brock
I am using flume 1.2.0.
About the batching : as per user guide "exec source" does have batch
option in 1.2.0 (param name:
batchSize and default value:20) and I
have tried it. Apparently it works fine. And file channel has parameter
"transactionCapacity" set
to 1000 by default. Is that the batch size of file channel?
Anyway even with increased batching I couldn't cross 110-150 KB/sec with
File Channel.
Could you please help me understanding questions I asked in the original
mail of this thread about
fsync lies. Because with disk which "apparently does fsync lie" I get 3
MB/sec in 1 flow.
I don't know whether that actually does "fsync lie" but there is
remarkable difference in fsync
performance on 2 machines which do have almost similar hardware.
Regards
Jagadish
On 10/22/2012 07:59 PM, Brock Noland wrote:
In this cae, it's best to think about FileChannel as if it were a
database. Let's pretend we are going to insert 1 million rows. If we
committed on each row, would performance be "good"? No, everyone
knows that when you are inserting rows in databases, you want to batch
100-1000 rows into a single commit, if you want "good" performance.
(Quoting good because it's subjective based on the scenario, but in
this case we mean lots of MB/second).
Part of the reason behind this logic is that when a database does a
commit, it does an fsync operation to ensure that all data is written
to disk and that you will not lose data due to a subsequent power loss.
FileChannel behaves *exactly* the same. If your "batch" is only a
single event, file channel will:
write single event
fsync
write single event
fsync
As such, if you want "good" performance with FileChannel, you must
increase your batch size, just like a database. If you have a
batchSize of say 100, then FileChannel will:
write single event 0
write single event 1
...
write single event 99
fsync
Which will result in much "better" performance. It's worth noting that
ExecSource in Flume 1.2, does not have a batchSize and as such each
event is written and then committed. ExecSource in flume 1.3, which we
will release soon, does have a configurable batchSize. If you want to
try that out you can build it from the flume-1.3.0 branch.
Brock
On Mon, Oct 22, 2012 at 8:59 AM, Brock Noland <[email protected]
<mailto:[email protected]>> wrote:
Which version? 1.2 or trunk?
On Monday, October 22, 2012 at 8:18 AM, Jagadish Bihani wrote:
Hi
This is the simplistic configuration with which I am getting
lower performance.
Even with 2-tier architecture (cat source - avro sinks - avro
source- HDFS sink)
I get the similar performance with file channel.
Configuration:
=========
adServerAgent.sources = avro-collection-source
adServerAgent.channels = fileChannel
adServerAgent.sinks = hdfsSink fileSink
# For each one of the sources, the type is defined
adServerAgent.sources.avro-collection-source.type=exec
adServerAgent.sources.avro-collection-source.command= cat
/home/hadoop/file.tsf
# The channel can be defined as follows.
adServerAgent.sources.avro-collection-source.channels = fileChannel
#Define file sink
adServerAgent.sinks.fileSink.type = file_roll
adServerAgent.sinks.fileSink.sink.directory =
/home/hadoop/flume_sink*
*
adServerAgent.sinks.fileSink.channel = fileChannel
adServerAgent.channels.fileChannel.type=file
adServerAgent.channels.fileChannel.dataDirs=/home/hadoop/flume/channel/dataDir5
adServerAgent.channels.fileChannel.checkpointDir=/home/hadoop/flume/channel/checkpointDir5
adServerAgent.channels.fileChannel.maxFileSize=4000000000
And it is run with :
JAVA_OPTS = -Xms500m -Xmx700m -Dcom.sun.management.jmxremote
-XX:MaxDirectMemorySize=2g
Regards,
Jagadish
On 10/22/2012 05:42 PM, Brock Noland wrote:
Hi,
I'll respond in more depth later, but it would help if you
posted your configuration file and the version of flume you are
using.
Brock
On Mon, Oct 22, 2012 at 6:48 AM, Jagadish Bihani
<[email protected]
<mailto:[email protected]>> wrote:
Hi
I am writing this on top of another thread where there was
discussion on "fsync lies" and
only file channel used fsync and not file sink. :
-- I tested the fsync performance on 2 machines (On 1 machine I
was getting very good throughput
using file channel and on another almost 100 times slower with
almost same hardware configuration.)
using following code
#define PAGESIZE 4096
int main(int argc, char *argv[])
{
char my_write_str[PAGESIZE];
char my_read_str[PAGESIZE];
char *read_filename= argv[1];
int readfd,writefd;
readfd = open(read_filename,O_RDONLY);
writefd = open("written_file",O_WRONLY|O_CREAT,777);
int len=lseek(readfd,0,2);
lseek(readfd,0,0);
int iterations = len/PAGESIZE;
int i;
struct timeval t0,t1;
for(i=0;i<iterations;i++)
{
read(readfd,my_read_str,PAGESIZE);
write(writefd,my_read_str,PAGESIZE);
*gettimeofday(&t0,0);**
**fsync(writefd);**
**gettimeofday(&t1,0);*
long elapsed = (t1.tv_sec-t0.tv_sec)*1000000 +
t1.tv_usec-t0.tv_usec;
printf("Elapsed time is= %ld \n",elapsed);
}
close(readfd);
close(writefd);
}
-- As expected it requires typically 50000 microseconds for
fsync to complete on one machine and 200 microseconds
on another machine it took 290 microseconds to complete on an
average. So is machine with higher
performance is doing a 'fsync lie'?
i
-- If I have understood it clearly; "fsync lie" means the data
is not actually written to disk and it is in
some disk/controller buffer. I) Now if disk loses power due to
some shutdown or any other disaster, data will
be lost. II) Can data be lost even without it ? (e.g. if it is
keeping data in some disk buffer and if fsync is being
invoked continuously then will that data can also be lost? If
only part -I is true; then it can be acceptable
because probability of shutdown is usually less in production
environment. But if even II is true then there is a
problem.
-- But on the machine where disk doesn't lie performance of
flume using File channel is very low (I have seen it
maximum 100 KB/sec even with sufficient DirectMemory
allocation.) Does anybody have stats about throughput
of file channel ? Is anybody getting better performance with
file channel (without fsync lies). What is the recommended
usage of it for an average scenario ? (Transferring files of
few MBs to HDFS sink continuously on typical hardware
(16 core processors, 16 GB RAM etc.)
Regards,
Jagadish
On 10/10/2012 11:30 PM, Brock Noland wrote:
Hi,
On Wed, Oct 10, 2012 at 11:22 AM, Jagadish Bihani
<[email protected]> <mailto:[email protected]>
wrote:
Hi Brock
I will surely look into 'fsync lies'.
But as per my experiments I think "file channel" is causing the issue.
Because on those 2 machines (one with higher throughput and other with
lower)
I did following experiment:
cat Source -memory channel - file sink.
Now with this setup I got same throughput on both the machines. (around 3
MB/sec)
Now as I have used "File sink" it should also do "fsync" at some point of
time.
'File Sink' and 'File Channel' both do disk writes.
So if there is differences in disk behaviour then even in the 'File Sink' it
should be visible.
Am I missing something here?
File sink does not call fsync.
Regards,
Jagadish
On 10/10/2012 09:35 PM, Brock Noland wrote:
OK your disk that is giving you 40KB/second is telling you the truth
and the faster disk is lying to you. Look up "fsync lies" to see what
I am referring to.
A spinning disk can do 100 fsync operations per second (this is done
at the end of every batch). That is how I estimated your event size,
40KB/second is doing 40KB / 100 = 409 bytes.
Once again, if you want increased performance, you should increase the
batch size.
Brock
On Wed, Oct 10, 2012 at 11:00 AM, Jagadish Bihani
<[email protected]> <mailto:[email protected]>
wrote:
Hi
Yes. It is around 480 - 500 bytes.
On 10/10/2012 09:24 PM, Brock Noland wrote:
How big are your events? Average about 400 bytes?
Brock
On Wed, Oct 10, 2012 at 5:11 AM, Jagadish Bihani
<[email protected]> <mailto:[email protected]>
wrote:
Hi
Thanks for the inputs Brock. After doing several experiments
eventually problem boiled down to disks.
-- But I had used the same configuration (so all software components
are
same in all 3 machines)
on all 3 machines.
-- In User guide it is written that if multiple file channel instances
are
active on the same agent then
different disks are preferable. But in my case only one file channel is
active per agent.
-- Only one pattern I observed that on the machines where I got better
performance have multiple disks.
But I don't understand how that will help if I have only 1 active file
channel.
-- What is the impact of the type of disk/disk device driver on
performance?
I mean I don't understand
with 1 disk I am getting 40 KB/sec and with other 2 MB/sec.
Could you please elaborate on File channel and disks correlation.
Regards,
Jagadish
On 10/09/2012 08:01 PM, Brock Noland wrote:
Hi,
Using file channel, in terms of performance, the number and type of
disks is going to be much more predictive of performance than CPU or
RAM. Note that consumer level drives/controllers will give you much
"better" performance because they lie to you about when your data is
actually written to the drive. If you search for "fsync lies" you'll
find more information on this.
You probably want to increase the batch size to get better performance.
Brock
On Tue, Oct 9, 2012 at 2:46 AM, Jagadish Bihani
<[email protected]> <mailto:[email protected]>
wrote:
Hi
My flume setup is:
Source Agent : cat source - File Channel - Avro Sink
Dest Agent : avro source - File Channel - HDFS Sink.
There is only 1 source agent and 1 destination agent.
I measure throughput as amount of data written to HDFS per second.
( I have rolling interval 30 sec; so If 60 MB file is generated in 30
sec
the
throughput is : -- 2 MB/sec ).
I have run source agent on various machines with different hardware
configurations :
(In all cases I run flume agent with JAVA OPTIONS as
"-DJAVA_OPTS="-Xms500m -Xmx1g -Dcom.sun.management.jmxremote
-XX:MaxDirectMemorySize=2g")
JDK is 32 bit.
Experiment 1:
=====
RAM : 16 GB
Processor: Intel Xeon E5620 @ 2.40 GHz (16 cores).
64 bit Processor with 64 bit Kernel.
Throughput: 2 MB/sec
Experiment 2:
======
RAM : 4 GB
Processor: Intel Xeon E5504 @ 2.00GHz (4 cores). 32 bit Processor
64 bit Processor with 32 bit Kernel.
Throughput : 30 KB/sec
Experiment 3:
======
RAM : 8 GB
Processor:Intel Xeon E5520 @ 2.27 GHz (16 cores).32 bit Processor
64 bit Processor with 32 bit Kernel.
Throughput : 80 KB/sec
-- So as can be seen there is huge difference in the throughput with
same
configuration but
different hardware.
-- In the first case where throughput is more RES is around 160 MB in
other
cases it is in
the range of 40 MB - 50 MB.
Can anybody please give insights that why there is this huge difference
in
the throughput?
What is the correlation between RAM and filechannel/HDFS sink
performance
and also
with 32-bit/64 bit kernel?
Regards,
Jagadish
--
Apache MRUnit - Unit testing MapReduce -
http://incubator.apache.org/mrunit/
--
Apache MRUnit - Unit testing MapReduce -
http://incubator.apache.org/mrunit/
