http://www.h2database.com/html/grammar.html#truncate_table
I would suggest you use a series of tables with one hour per table. Then build a view over those tables for your select queries to operate on. Then truncate the oldest tables as necessary. On 2012-02-10 02:48, jim wrote:
Hi Thomas, You also mentioned truncating a table: -- Does that incur copying the truncated rows to the transaction log? -- How can I move rows to the table without incurring a transaction copy on delete? -- Is there some kind of INSERT + DELETE syntax to simulate a block move? otherwise doing an insert into a new table means I have to delete the rows from the old table and incur the transaction log copy. ** This is a continuation of my previous two posts today. ** Thanks, Jim McArdle On Feb 9, 2:16 pm, jim<[email protected]> wrote:correction on text in item #2: As an example, the first 14 deletes at 1000 rows average 2000 rows/ sec. However the 15th 1000 row delete takes 200 secs to complete. ( 14*(1000) + 1000)/(14*.5 + 200) = 72 rows/sec). -- Jim McArdle On Feb 9, 9:11 am, jim<[email protected]> wrote:Hi Thomas, Thanks for the fast and thorough reply. 1) The sensor data table is basically a FIFO queue with new rows being added to the end and the oldest rows being deleted from the beginning. We don't delete anything in the middle at any time. 2) Deletes don't start until the 10 day range has been achieved. It is at that time that I see the average 60-70rows/sec delete rate after 15000 rows has been deleted. This makes me think that deletes are being queued until there is enough to delete and then the actual delete processing kicks in halting all queries until it is finished. I tried the idea of deleting smaller blocks of rows at 100 rows per delete. What I found is that when you've deleted 15000 in total then the server goes into a kind of garbage cleanup. As an example, the first 14 deletes at 1000 rows average 200 rows/sec. However the 15th 1000 row delete takes 200 secs to complete. ( 14*(1000) + 1000)/(14*.5 + 200) = 72 rows/sec). During that time I'm also adding 15000 rows of new data as data is continually streaming in. However, when I did the measurements above no data was streaming in. It was just me, H2 and the H2 shell sparring. The rownum<999 expression the 999 was meant to be a placeholder for whatever number I used. Yes the deletes are in a loop with small sleeps to allow the other queries to get processed. I trying to performance tune so that the enduser query doesn't take too long and waiting upto 3-5 mins for a small query of 48 to 96 rows is too long when I've seen it come back in 10 to 20 secs previously. 3) Based on #1 and #2 I don't fragmentation has become an issue as this happens as I reach the 10 day storage range. 4) Your suggestion of blocking the data into tables by day sounds interesting but it becomes an architectural issue for me as I would now have to do joins across tables to get at the data. -- Is dropping a table significantly faster than deleting rows from it? -- Isn't the table drop considered a transaction so that the dropped rows will need to be copied to the transaction log? -- If I create tables for each half hour time period (50K rows) or I create tables for each day (48 * 50k) will the time be significantly different for dropping the table? -- It seems that using joins will shift the time burden to the SELECT query slowing it down significantly? 5) I will try the -tcpShutdownForce option to see if things terminate quicker. 6) I will try using a profiling tool. Do you have any open source suggestions? My profiling has been mostly in app query timing and shell timing. 7) Is there any trace I can use on the server to see what its doing while its doing it? Thanks for your time, Jim McArdle On Feb 8, 11:27 pm, Thomas Mueller<[email protected]> wrote:Hi, What I'm seeing is that all the queries run quickly with the exceptionof deletes.Deleting using the primary key should help. Another solution is to use multiple tables, so that instead of deleting a number of rows you could drop or truncate a table. times for the 15 deletes and it averages out to 60-70 rows/sec. Possibly you need to defragment the database. To do that, use SHUTDOWN DEFRAG. There is also an option to only defragment partially.-- Is there a way to do smaller block deletes and to force the H2 Server to do the database cleanup?You could delete less rows at a time using DELETE ... WHERE ROWNUM()< 100.-- Could ANALYZE or some option on DELETE force a cleanup for smaller block deletes?The statement ANALYZE calculates the selectivity as documented, nothing else.LOB files -- How can these be eliminated?Upgrade to the latest version. -- Do I need to move to a newer version of H2 for lobs in databasestorage?You actually need to re-build the database to make them go away.Lastly, our client apps and the H2 server are stopped abruptly when they aren't responding and upon restart for a 5-10 day database H2 Server takes an inordinate amount of time to startup which I suspect is rollback recovery of broken transactions.You could get a few full thread dumps to find out what is happening. I usually use jps -l jstack -l<pid>We do use the -tcpShutdown but it doesn't seem to shutdown the serveras quickly as needed. You could use -tcpShutdownForce as documented.The sql I use is: DELETE FROM MySensorTable WHERE SweepNo<99999 andrownum<999; That means at most 998 rows are deleted at any time.The issue I'm seeing is that it looks like delete changes are being queued up and then processed after 15000 rows have been deleted.I don't understand, do you mean the "rownum<999" didn't work? Or did you call the DELETE statement multiple times in a loop?I realize that deletes copy the row to the transaction log in case of failure or disconnectActually, it's a bit more complicated than that. In most cases, I found the best way to deal with performance problems is to use a profiling tool. Sometimes the problem is in a completely different area than originally thought. Regards, Thomas
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