[h2] Are order of results always the same?

[Adam McMahon]

Hi,

It looks like the results of a querry are always given back in the same 
order.  Is this always true?  I know the order of a returned result is not 
the same as the insertion order.  But if a query is performed, and then 
repeated, will the result set be in the order (assuming the relevant tables 
have not changed?

Thanks,

-Adam 

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[h2] group by query and memory consumption

[Michaël Michaud]

Hello,

Is there a way to avoid OutOfMemory with large "group by" queries.
I have a large table and want to group rows according to id column.
Here is a simple test case to reproduce the problem (I use H2GIS 1.2.3
based on H2 1.4.188 because original query is a spatial query)

jvm : -Xmx512M

CREATE TABLE A(id integer);
@loop 2000 INSERT INTO A VALUES (?/*rnd*/ / 10);
SELECT id, count(*) FROM A GROUP BY id LIMIT 1000;
-> OOM

In my initial query, query is more complex, rows are more complex,
aggregate function is a spatial function... so that I reach OOM 
with only 6M rows and as much as 16G.

Thanks for your help and for a great software,

Michaël


 


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Re: [h2] Maven SNAPSHOT artefacts

[Sergi Vladykin]

Thanks a lot! Will try it.

Sergi
On Nov 24, 2015 9:20 AM, "Thomas Mueller" 
wrote:

> Hi,
>
> What I have so far is an automated 1.0-SNAPSHOT build:
>
>
> http://h2database.com/m2-repo/com/h2database/h2/1.0-SNAPSHOT/h2-1.0-SNAPSHOT.pom
>
> Regards,
> Thomas
>
>
> On Fri, Nov 20, 2015 at 7:25 AM, Sergi Vladykin 
> wrote:
>
>> Any news? I'm providing quite a few changes in H2 lately and want to do
>> more testing
>> (going to provide a couple more pull requests soon). It would be nice to
>> have
>> a Maven access to a nightly build.
>>
>> Sergi
>>
>>
>> 2015-11-06 11:54 GMT+03:00 Thomas Mueller :
>>
>>> Hi,
>>>

 You have to set SNAPSHOT for maven as SNAPSHOT jar are automatically
 re-downloaded every day (or forced with -U command)

>>>
>>> OK, I didn't know, there _are_ some hardcoded rules... It makes sense to
>>> use SNAPSHOT then.
>>>

>>> SNAPSHOT is not a problem with OSGi. In the MANIFEST you have to replace
 1.4.191-SNAPSHOT by 1.4.191.SNAPSHOT and it is ok (this is what maven
 bundle plugin do).

>>>
>>> The problem I was talking about is that for OSGi, 1.4.191.SNAPSHOT is
>>> _newer_ than 1.4.191, but it should be older. So once you install
>>> 1.4.191.SNAPSHOT, installing the released version later on will be ignored,
>>> because it is "older". See also
>>> http://versionatorr.appspot.com/?a=1.4.191.SNAPSHOT=1.4.191
>>>
>>> But OSGi is not as popular as Maven, so it makes sense to use SNAPSHOT
>>> then.
>>>
>>> Regards,
>>> Thomas
>>>
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[h2] When is the H2 1.4 version GA release?

[Yadlapalli Vasu]

Hi,

We are using the H2 database as our in-memory cache and having lot of 
performance issues with MVCC=TRUE. We tested the 1.4.190 beta build with 
MULTI_THREADED enabled and observed huge performance improvements and 
concurrent transaction commits.

It would be really helpful if anyone let us know the GA release for 1.4, we 
are eagerly waiting to use 1.4 in our production.

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Re: [h2] When is the H2 1.4 version GA release?

[Noel Grandin]

Hi

Even when 1.4 goes GA, I'm afraid the MULTI_THREADED stuff will still be experimental. There are some bugs hiding in 
there that we have never quite been able to kill - it works fine for some people, but not for others.


Regards, Noel.

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Re: [h2] Are order of results always the same?

[Noel Grandin]

You can't rely on that. If you need order, you need to enforce it with an ORDER 
BY clause.

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[h2] Corrupted ?

[ivan]

When I using the recover tool to output the transaction log... this is what 
I get. 
and I can't start my database. after I killed the Java

0 fileHeader 
H:2,block:27c38,blockSize:1000,chunk:10b6,created:1513314310e,format:1,version:10b6,fletcher:121921b7
01000 fileHeader 
H:2,block:27c38,blockSize:1000,chunk:10b6,created:1513314310e,format:1,version:10b6,fletcher:121921b7

02000 chunkHeader 
chunk:bfc,block:2,len:9,map:49,max:a500,next:b,pages:29,root:2ff15158d,time:272c5eb,version:bfc
+0009e node, map 42, 4 entries, 684 bytes, maxLen 300
190354 children @ chunk bfb +0034a
232366 children @ chunk bfb +a7ae3
261510 children @ chunk bfb +0002b2435
217332 children @ chunk bfc +0034a
+0034a node, map 42, 4 entries, 684 bytes, maxLen 300
50008 children @ chunk bfb +0004f05a1
43893 children @ chunk bfb +00056695e
69881 children @ chunk bfb +0005c276b
53550 children @ chunk bfc +005f6

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