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From Lukasz <flo...@intercel.com.pl>
Subject Re: Processing huge heap dump.
Date Thu, 14 Jan 2010 17:21:15 GMT
Hi Steve, Stuart,

In last two days I was trying to move further.

I tried to prepare some workaround for incorrect length.
First idea was to utilize the fact that integer overflow probably took 
place, so I tried to search for 0x2c just at overflow points (probably 
quite brittle approach). But it turned out, that in my heap dumps (both 
real one and prepared for development purposes) there is no 0x2c byte 
after/at the end of the dump.
I've noticed however that for both dumps the heap record ends at the end 
of the file. Probably it is not general rule, but for my purposes it 
should be enough, so I changed kato sources slightly to utilize this and 
decided to move further.

So far I have some code which extracts static data from dump (strings, 
classes) and searches for instances of given class.
I have run it against real dump. It took around 40 min (to get static 
data) and 50 min (to find instances), which is not bad I think.
I didn't made careful reasoning about performance but CPU (not I/O) 
looked to be a bottleneck. Performance also looked to be quite stable 
across whole dump.

60GB dump was extracted for core file using jmap (I don't remember 
exactly from which version of java this jmap came from, but for sure it 
was Java 1.6).
Following JVM version was dumped to core file:
java version "1.6.0_10"
Java(TM) SE Runtime Environment (build 1.6.0_10-b33)
Java HotSpot(TM) 64-Bit Server VM (build 11.0-b15, mixed mode)

I was also suspecting that heap dump segments were introduced to handle 
+4GB heap sizes, but it looks like sometimes it can not be a case.

Anyway, it is nice that I was able to go through whole dump without any 
error.

Regards
Lukasz

Steve Poole wrote:
>  Hi Lukasz,
>
>  You say your  hprof format is 1.0.1   so , according to the information I
> have about hprof format,  that means your won't have any heap dump segments
> in your file.  Apparently they are in the  1.0.2 format which is a Java 6
> addition and is only used when the heap is too big for the old format to
> cope with.
>
> What JVM and OS are you using to produce this dump?
>
> On Tue, Jan 12, 2010 at 6:17 PM, Stuart Monteith <stukato@stoo.me.uk> wrote:
>
>   
>> Hi,
>>
>>
>> You are quite right, 4 bytes for the record length. If we had the file
>> format wrong for 64 bit
>> hprof dumps we'd not be able to read any dump, so it must be an overflow of
>> the record length.
>> In that case, the only possible solution I can think of would be for us to
>> change to code to search
>> for the HEAP DUMP END record (tagged 0x2c) to detect the end of the HEAP
>> DUMP.
>>
>> Of course, there was some puzzling over the difference between HEAP DUMP
>> SEGMENT (0x1c) and HEAP DUMP
>> (0x0c) before.
>>
>> I'd expect we'd get:
>>
>>    HEAP DUMP
>>        heap dump records....
>>    HEAP DUMP END
>>
>> or
>>
>>    HEAP DUMP SEGMENT
>>        heap dump records
>>    HEAP DUMP SEGMENT
>>        heap dump records
>>       :      :
>>    HEAP DUMP END
>>
>>
>> If we ignore the record size for the HEAP DUMP and calculate it ourselves,
>> we might have more luck.
>>
>> Regards,
>>    Stuart
>>
>>
>>
>> Lukasz wrote:
>>
>>     
>>> Hello,
>>>
>>> Since performance looks not bad after changing array size, today I have
>>> tried to process my 60GB heap dump. Unfortunately, very fast I've ended with
>>> exception:
>>> Exception in thread "main" java.lang.IllegalArgumentException: range
>>> -1293366370 is less than 0
>>> at
>>> org.apache.kato.common.SubsetDataProvider.<init>(SubsetDataProvider.java:29)
>>>
>>> at
>>> org.apache.kato.hprof.datalayer.HProfFile$HPROFRecordProvider.getCurrentElement(HProfFile.java:487)
>>>
>>> at
>>> org.apache.kato.hprof.datalayer.HProfFile$HPROFRecordProvider.getCurrentElement(HProfFile.java:437)
>>>
>>> at
>>> org.apache.kato.common.BitMaskMappingArray.get(BitMaskMappingArray.java:56)
>>> at org.apache.kato.hprof.datalayer.HProfFile.getRecord(HProfFile.java:784)
>>> ... (my code) ...
>>>
>>> It looks like range of HeapDumpHProfRecord had value: -1293366370.
>>>
>>> Following is the part of the dump which I believes is responsible for that
>>> (B2 E8 CB 9E):
>>> 0055DD84 25 00 00 2A │ B7 AE 22 06 │ 80 00 00 00 │ 01 00 00 2A │ B7 AE
20
>>> 0B │ 88 02 00 00 │ 00 00 00 00 │ 00 18 00 00 │ 23 26 00 00
>>> 0055DDA8 2A B7 B0 A1 │ 64 28 00 00 │ 00 01 00 00 │ 2A B7 B0 33 │ EA F8
0C
>>> 00 │ 00 00 00 B2 │ E8 CB 9E 20 │ 00 00 2A B7 │ B0 DE AF C8
>>> 0055DDCC 00 00 00 01 │ 00 00 2A B7 │ AE 22 0F 20 │ 00 00 2A AA │ BE 21
3D
>>> 28 │ 00 00 00 00 │ 00 00 00 00 │ 00 00 2A AA │ BE 25 B7 D8
>>>
>>> What is interesting hprof file format reserves only 4 bytes for length of
>>> a record, which allows to express record whose size is at most 4GB (assuming
>>> unsigned 4 bytes).
>>>
>>> My dump's version is: JAVA PROFILE 1.0.1
>>>
>>> Regards
>>> Lukasz
>>>
>>>
>>> Lukasz wrote:
>>>
>>>       
>>>> Hi Stuart, Steve,
>>>>
>>>> I've taken deeper look into code. I still didn't trace carefully index
>>>> calculation in classes BitMaskMappingArray and ArrayBitMaskMappingStrategy,
>>>> but I managed to improve performance by increasing arrays size in those
>>>> classes (which is set in HProfFile class).
>>>>
>>>> If I understand code correctly, when capacity of BitMaskMappingArray will
>>>> be exhausted bucketSize is doubled, which in turn causes that more reads
>>>> (even cached) is required to set position of
>>>> IDataProvider/IArrayEntryProvider.
>>>>
>>>> Following are loading time results for default array size (1000) and
>>>> increased (1000000). Test ran against generated dump file (5000000 instances
>>>> of Data).
>>>> Default (1000):
>>>> HeapSubRecord: 100000 (866ms, 4215kB)
>>>> HeapSubRecord: 200000 (1716ms, 7879kB)
>>>> HeapSubRecord: 300000 (2833ms, 11263kB)
>>>> HeapSubRecord: 400000 (3889ms, 14283kB)
>>>> HeapSubRecord: 500000 (3893ms, 17319kB)
>>>> HeapSubRecord: 600000 (7248ms, 20479kB) (here probably buckedSize was
>>>> doubled)
>>>> HeapSubRecord: 700000 (7721ms, 23531kB)
>>>> HeapSubRecord: 800000 (7729ms, 26567kB)
>>>> HeapSubRecord: 900000 (7731ms, 29671kB)
>>>> HeapSubRecord: 1000000 (7704ms, 32731kB)
>>>> ... (I didn't wait until end)
>>>>
>>>> Increased(1000000):
>>>> HeapSubRecord: 100000 (622ms, 17809kB)
>>>> HeapSubRecord: 200000 (309ms, 20345kB)
>>>> HeapSubRecord: 300000 (283ms, 23861kB)
>>>> HeapSubRecord: 400000 (274ms, 27921kB)
>>>> HeapSubRecord: 500000 (269ms, 29957kB)
>>>> HeapSubRecord: 600000 (264ms, 31993kB)
>>>> HeapSubRecord: 700000 (272ms, 36097kB)
>>>> HeapSubRecord: 800000 (288ms, 37739kB)
>>>> HeapSubRecord: 900000 (263ms, 39835kB)
>>>> HeapSubRecord: 1000000 (259ms, 41931kB)
>>>> HeapSubRecord: 1100000 (300ms, 44773kB)
>>>> HeapSubRecord: 1200000 (283ms, 46901kB)
>>>> HeapSubRecord: 1300000 (291ms, 49029kB)
>>>> HeapSubRecord: 1400000 (328ms, 53801kB)
>>>> HeapSubRecord: 1500000 (259ms, 53801kB)
>>>> HeapSubRecord: 1600000 (272ms, 58125kB)
>>>> HeapSubRecord: 1700000 (264ms, 60293kB)
>>>> HeapSubRecord: 1800000 (264ms, 62473kB)
>>>> HeapSubRecord: 1900000 (361ms, 61373kB)
>>>> HeapSubRecord: 2000000 (274ms, 63105kB)
>>>> ...
>>>> HeapSubRecord: 9000000 (284ms, 231969kB)
>>>> HeapSubRecord: 9100000 (272ms, 233597kB)
>>>> HeapSubRecord: 9200000 (281ms, 236357kB)
>>>> HeapSubRecord: 9300000 (274ms, 240469kB)
>>>> HeapSubRecord: 9400000 (279ms, 244541kB)
>>>> HeapSubRecord: 9500000 (269ms, 246549kB)
>>>> HeapSubRecord: 9600000 (279ms, 250565kB)
>>>> HeapSubRecord: 9700000 (265ms, 252573kB)
>>>> HeapSubRecord: 9800000 (279ms, 256629kB)
>>>> HeapSubRecord: 9900000 (265ms, 258669kB)
>>>> HeapSubRecord: 10000000 (463ms, 263997kB)
>>>> (end)
>>>>
>>>> i.e. my 60GB dump file contains more than 1 100 000 000 of objects (if I
>>>> remember correctly).
>>>>
>>>> Regards
>>>> Lukasz
>>>>
>>>>
>>>> Stuart Monteith wrote:
>>>>
>>>>         
>>>>> The hprof dump reader spends a lot of time reading the whole file, for
>>>>> various reason.
>>>>> The indices it has in memory are constructed through an initial read,
>>>>> and this is also
>>>>> the source of the memory usage. In addition, there is some correlation
>>>>> to be done which
>>>>> also takes up time, and induces yet more reading.
>>>>>
>>>>> I'm sure some work could be done to improve the performance further,
but
>>>>> we'll have to
>>>>> look at the tradeoff between diskspace and memory usage. The hprof file
>>>>> format itself
>>>>> is what it is, however, and we have no influence over that. The CJVMTI
>>>>> agent is has lots of
>>>>> room for improvement, but I suspect its potential for improvement is
>>>>> unlikely to be much better
>>>>> than existing hprof implementations. The built-in JVM hprof dumper will
>>>>> probably be a hard act
>>>>> to follow.
>>>>>
>>>>> The HProf implementation is not thread-safe. Realistically, I think it
>>>>> is something that ought to
>>>>> be considered once things are more mature. There will be algorithms that
>>>>> can deal with the JVM
>>>>> structure sensible.
>>>>>
>>>>> And thanks Lukasz, it's great to have your input.
>>>>>
>>>>> Regards,
>>>>> Stuart
>>>>>
>>>>>           
>>>>         
>> --
>> Stuart Monteith
>> http://blog.stoo.me.uk/
>>
>>
>>     
>
>
>   


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