1.4 beta creates much bigger database file

[Steve McLeod]

Hi Thomas,

I've tried my desktop app with the new MV store in 1.4.177. After loading a significant amount of data, the database file is 3 times the size, compared to H2 1.3.176

Here are the file sizes, in both cases after the app has stopped:

pokercopilot.h2.db  302,018,560  bytes

pokercopilot.mv.db 999,120,896  bytes

Is that expected? If not, what can I do to help locate the problem?

Regards,

Steve

[Thomas Mueller]

Hi,

Probably it's due to the long default retention time, see http://h2database.com/html/grammar.html#set_retention_time - try adding ";retention_time=1000" to the database URL, and tell us if and how much this reduced the size.

Regards,

Thomas

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[Steve McLeod]

Hi Thomas,

Thanks for the suggestion. I tried adding ";retention_time=1000" to the URL, and this resulted in a small improvement.

pokercopilot.h2.db  302,018,560  bytes

pokercopilot.mv.db 999,120,896  bytes

pokercopilot.mv.db with RETENTION_TIME=1000:  811,728,896 bytes

These numbers all reflect a loading of data in a newly created database that consisted of roughly 2,400,000 INSERTS and UPDATES with plenty of SELECTS and almost no DELETES. After the loading was complete, I let the application keep running with the database open for a few minutes, then close the application and therefore the database.

Here is the full JDBC url I'm using:

jdbc:h2:/Users/steve/Library/Application Support/com.barbarysoftware.pokercopilot/database/pokercopilot;DATABASE_EVENT_LISTENER='com.barbarysoftware.pokercopilot.database.DatabaseListener';COMPRESS_LOB=DEFLATE;CACHE_SIZE=65536;RETENTION_TIME=1000

Let me know if there is anything else I can do to help diagnose this.

Regards,

Steve

[Thomas Mueller]

Hi,

Hm, that didn't help much. Could you send me the (compressed) database files please? If it's too big, what is the compressed size of the files?

Regards,

Thomas

[Steve McLeod]

Hi Thomas,

I've sent a link to file privately to your email address.

Regards,

Steve

[Thomas Mueller]

Hi,

Thanks a lot for the database! I know what the problem is now, but I couldn't fix it yet. The database file (pokercopilot2.mv.db) has about 181 MB of "live" data, the rest (about 78%) is not used. The mechanism to get rid of the unused space is not working as it should for this case (I think the problem is that b-tree nodes are not processed correctly). This will be fixed in the next release.

Regards,

Thomas

[Steve McLeod]

Hi Thomas,

Great! Glad I could help make your superb product even better.

[Steve McLeod]

Hi Thomas,

I tested the same large data import with H2 1.4.178, and there is no improvement over H2 1.4.177.

Here are the file sizes, in both cases after the app has stopped:

H2 1.3.176: pokercopilot.h2.db  301,669,352  bytes

H2 1.4.178: pokercopilot.mv.db 1,023,037,440  bytes

Let me know what I can do to help.

Regards,

Steve

[Thomas Mueller]

Hi,

The database file should shrink if you run "shutdown defrag".

The current compact algorithm is quite inefficient, that means the databases file is quite big on average. The highest priority is still to ensure it always works correctly, and when that's done I will work on more efficiently re-using disk space and specially compact the file faster when closing the database.

Could you send me the new database file? It would be nice to have a real-world database file to test this. The last file you sent helped a lot, thanks to it I found some problems that completely prevented the file to shrink.

Regards,

Thomas

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[Steve McLeod]

Hi Thomas,

I've sent you a private email with a link to the new database file, made with H2 1.4.178

Regards,

Steve

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[Thomas Mueller]

Hi,

Some initial results: you can shrink the database by running "shutdown compact" or "shutdown defrag". Each time this is run, it shrinks a few MB (up to some point, of course). This works, but it's relatively slow. Now the task is to make it faster. There are two ways: shrink it fully to the minimum size, and shrink it incrementally (like now) but faster. I'm working on that now.

Regards,

Thomas

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[Thomas Mueller]

Hi,

Version 1.4.184 should produce smaller database files than previous version (1.4.x - 1.4.182), maybe half or a third of the old file size. It would be great to get some real-world results!

Regards,

Thomas

[Steve McLeod]

Hi Thomas,

The database file size in 1.4.184 is much, much better than in earlier 1.4.x releases.

I've done some trials and these are my findings:

1.3.176: Fully loaded database after shutdown is 317 Mb

1.4.184: Fully loaded database after shutdown is 380 Mb

This seems reasonable.

[Thomas Mueller]

Hi,

OK, that's nice! There is still quite a lot of room for improvements, and I don't consider this completely fixed, but will not work on it with very high priority any longer.

Regards,

Thomas

[Damien Coraboeuf]

Hi,

Speaking of real world example - we are using H2 1.4.x to hold results for a continuous delivery chain. With 1.4.177, our database was > 600 Mb, and after a 'shutdown defrag', we went down to... 11 Mb. We switched to 1.4.184 but now, the database has grown up to 1.7 Gb. That's a serious issue for us :(

The URL we use is:

jdbc:h2:/opt/ontrack/database/data;MODE=MYSQL

Damien.

[Damien Coraboeuf]

I have replaced by BLOB columns by BINARY(32000) ones (more than enough in our case). After exporting the database in SQL ('script' command), recreating a blank database and reimporting the SQL ('runscript'), I went from 1.7 Gb to 17 Mb.

I'll monitor the database in the next days to see if the inflation starts again.

Damien.

[Max Lord]

I also had problems with an mvstore db growing out of control (about 3GB for 1M rows). I updated to 1.4.184, reimported, and it was much smaller (100MB). 

So the recent changes have had a very positive effect. 

Unfortunately, I was using 1.4.178 because that was the current jar bundled with the jdbc-h2 ruby gem. That version doesn't seem like such a good default. 

[Damien Coraboeuf]

FYI, we were using 1.4.184 together with a JDK 1.8.0u11, on a CentOS 6, and the database kept growing by chunks of ~ 10 MB. We have upgraded to JDK 1.8.0u31, and although the file keeps growing, it is now by tiny chunks of kilobytes. So much better. I just hope there is some kind of runtime cleanup going on, because it would still go over 1.0 GB in 30 days :(

Is there a way to launch some SQL commands at runtime to make the database shrink?

Damien.

[Thomas Mueller]

Hi,

Disk space is re-used after 45 seconds (the default retention time). Disk space should stabilise at some point, unless if you add more and more data.

"checkpoint" should reduce disk space usage, but you may need to call it a few times. 

Regards,

Thomas

[Damien Coraboeuf]

Actually,

I was using the Tomcat JDBC pool with the default settings. The connection within the pool were never released - and it seems this prevented H2 to do its cleanup. After I've put the maxAge property on the pool (auto release after 10 minutes), the problem disappeared. The database file grows steadily but comes down to a normal size every 10 minutes.

I'd wish the database would not grow as fast, but it's already much better.

Damien.

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