RE: Avoid locking on DELETE

[Jerry Lampi]

ion.close();
//
System.out.println("totalRowsDeleted="+nbrFormatter.format(totalRowsDeleted));
} catch (SQLException sqle) {
  sqle.printStackTrace();
  while(sqle != null) {
String logMessage = "\n SQL Error: " + 
sqle.getMessage() + "\n\t\t"
  + "Error code: " + 
sqle.getErrorCode() + "\n\t\t"
  + "SQLState: "   + 
sqle.getSQLState() + "\n";
System.out.println(getLogPrefix() + logMessage);
sqle = sqle.getNextException();
  }
} catch (Exception e) {
  System.out.println("Exception in doIncrementalTimePurge(): " 
+ e);
  e.printStackTrace();
}
return totalRowsDeleted;
  }

  private static long getTimeToAddToIntervalBasedOnRowsdDeleted(int 
rowsDeletedThisIteration,
int 
prevIterationRowsDeleted) {
long oneMinuteMs = 6; // (60*1000)
long returnDurationMs = oneMinuteMs*60; // 1 hour default
if(rowsDeletedThisIteration > 2000) {
  returnDurationMs = oneMinuteMs*15; // 15 minutes
} else if(rowsDeletedThisIteration > 1500) {
  returnDurationMs = oneMinuteMs*30; // 30 minutes
} else if(rowsDeletedThisIteration > 1000) {
  returnDurationMs = oneMinuteMs*45; // 45 minutes
} else if(rowsDeletedThisIteration > 0) {
  if(rowsDeletedThisIteration > 500) {
returnDurationMs = oneMinuteMs*60; // 1 hour
  } else if(rowsDeletedThisIteration > 250) {
returnDurationMs = 
((oneMinuteMs*60)*1)+(oneMinuteMs*15); // 1 hour, 15 minutes
  } else if(rowsDeletedThisIteration > 125) {
returnDurationMs = 
((oneMinuteMs*60)*1)+(oneMinuteMs*30); // 1 hour, 30 minutes
  } else { // fewer than 125 records deleted, so increase 
interval
returnDurationMs = 
((oneMinuteMs*60)*1)+(oneMinuteMs*45); // 1 hour, 45 minutes
  }
} else { // zero rows deleted...
  if(prevIterationRowsDeleted <= 0) { // if we got two 
consecutive 0 row deletions...
returnDurationMs = (oneMinuteMs*60)*3; // 3 hours
          } else {
returnDurationMs = (oneMinuteMs*60)*2; // 2 hours
  }
}
return returnDurationMs;
  }
Jerry

From: Peter 
Sent: Wednesday, October 16, 2019 10:26 AM
To: derby-user@db.apache.org
Subject: Re: Avoid locking on DELETE

Hi Peter,

Thanks.

This procedure with disabling the autocommit is indeed simpler than I had 
before via "DELETE FROM mytable WHERE id IN (...)" but the delete itself takes 
longer (5-6 times) and I do not see differences with different batch sizes.

I've also benchmarked this process against postgresql and derby seems to be 
much slower here. Will investigate more as migrating is also a risk.

Regards
Peter

On 16.10.19 14:03, Peter Ondruška wrote:
You would need to test various scenarios. First I would propose larger batch 
size (N thousands of rows). Are you sure you execute deletes in batches? You 
should have autocommit off, execute N times delete statement, commit, repeat. 
Pseudo code (I am on mobile phone):

1. Acquire connection
2. Set connection autocommit to false
3. Create prepared statement with delete, DELETE FROM WHERE primary key = ?
4. Create set of primary keys to be deleted
5. Iterate set (4.) with adding those keys to delete statement (3.) as batch
6. When you reach batch size or end of key set execute batch and commit, 
continue (5.)

In my case with slow disk this really performs better and should avoid your 
issue as well.

Peter

On Mon, 7 Oct 2019, 22:11 Peter, 
mailto:tableyourt...@gmail.com>> wrote:
Hi Peter,

Thanks! I have implemented this and indeed the maximum delays are lower but the 
time for a delete batch to complete takes now longer (roughly 3-4 times; for 
batchSize=500, total deleted items around ~1). The problem is likely that I 
have VARCHAR for the ID column.

If I increase the frequency of issuing the original DELETE statement:

DELETE FROM mytable WHERE created_at < ?

Won't it have a similar effect due to smaller batches?

Regards
Peter

On 07.10.19 16:31, Peter Ondruška wrote:
In my case I have two separate steps. First SELECT primary keys of those 
records to be deleted (in your case SELECT id FROM mytable WHERE created_at < 
some_fixed_millis). And then I issue DELETE for those primary keys in batches 
of N statements (N being configuration paramet

Re: Avoid locking on DELETE

[Peter]

Hi Peter,

Thanks.

This procedure with disabling the autocommit is indeed simpler than I
had before via "DELETE FROM mytable WHERE id IN (...)" but the delete
itself takes longer (5-6 times) and I do not see differences with
different batch sizes.

I've also benchmarked this process against postgresql and derby seems to
be much slower here. Will investigate more as migrating is also a risk.

Regards
Peter

On 16.10.19 14:03, Peter Ondruška wrote:
> You would need to test various scenarios. First I would propose larger
> batch size (N thousands of rows). Are you sure you execute deletes in
> batches? You should have autocommit off, execute N times delete
> statement, commit, repeat. Pseudo code (I am on mobile phone):
>
> 1. Acquire connection
> 2. Set connection autocommit to false
> 3. Create prepared statement with delete, DELETE FROM WHERE primary
> key = ?
> 4. Create set of primary keys to be deleted
> 5. Iterate set (4.) with adding those keys to delete statement (3.) as
> batch
> 6. When you reach batch size or end of key set execute batch and
> commit, continue (5.)
>
> In my case with slow disk this really performs better and should avoid
> your issue as well.
>
> Peter
>
> On Mon, 7 Oct 2019, 22:11 Peter,  > wrote:
>
> Hi Peter,
>
> Thanks! I have implemented this and indeed the maximum delays are
> lower but the time for a delete batch to complete takes now longer
> (roughly 3-4 times; for batchSize=500, total deleted items around
> ~1). The problem is likely that I have VARCHAR for the ID column.
>
> If I increase the frequency of issuing the original DELETE statement:
>
> DELETE FROM mytable WHERE created_at < ?
>
> Won't it have a similar effect due to smaller batches?
>
> Regards
> Peter
>
> On 07.10.19 16:31, Peter Ondruška wrote:
>> In my case I have two separate steps. First SELECT primary keys
>> of those records to be deleted (in your case SELECT id FROM
>> mytable WHERE created_at < some_fixed_millis). And then I issue
>> DELETE for those primary keys in batches of N statements (N being
>> configuration parameter). You could create stored procedure for
>> this with two parameters (some_fixed_millis, batch_size).
>> Your idea DELETE WHERE SELECT and limiting rows needs to be run
>> for every DELETE step making unnecessary read I/O.
>>
>>
>> On Mon, 7 Oct 2019 at 14:10, Peter > > wrote:
>>
>> Hi Peter,
>>
>> Thanks a lot for the suggestion.This would be nice if it
>> performs better.
>>
>> Is the idea to split one request into smaller parts or will
>> "Select+Delete IDs" just perform better?
>>
>> And regarding the latter option - is this possible in one SQL
>> request? So something like
>>
>> DELETE FROM mytable WHERE id IN 
>>
>> ( SELECT id FROM mytable WHERE created_at < some_fixed_millis OFFSET 
>> 0 ROWS FETCH NEXT 1000 ROWS ONLY )
>>
>>
>> And then loop through the results via changing OFFSET and
>> ROWS? (Btw: the column created_at is indexed)
>>
>> Or would you recommend doing this as 2 separate statements in
>> Java/JDBC? Or via maybe even just issuing the original DELETE
>> request more frequent?
>>
>> Regards
>> Peter
>>
>> On 06.10.19 03:50, Peter Ondruška wrote:
>>> Peter, try this if it makes a difference:
>>>
>>> 1. Select entries to be deleted, note their primary keys.
>>> 2. Issue delete using keys to be deleted (1.) and use short
>>> transaction batches.
>>>
>>> On Sun, 6 Oct 2019, 01:33 Peter, >> > wrote:
>>>
>>> Hi,
>>>
>>> I have a table "mytable" with columns "id", "created_at"
>>> and "json"
>>> (VARCHAR, BIGINT, LONG VARCHAR), where data is coming in
>>> like new 200k
>>> entries every hour and I would like to keep only entries
>>> of the last 1
>>> or 2 hours. It is expected behaviour for the user if too
>>> old entries
>>> gets lost as it is some kind of a LRU cache.
>>>
>>> The current solution is to delete entries older than 4
>>> hours every 30
>>> minutes:
>>>
>>> DELETE FROM mytable WHERE created_at < ?
>>>
>>> I'm using this in a prepared statement where ? is "4
>>> hours ago" in
>>> milliseconds (new DateTime().getMillis()).
>>>
>>> This works, but some (not all) INSERT statement get a
>>> bigger delay in
>>> the same order (2-5 seconds) that this DELETE takes,
>>> which is ugly.
>>> These INSERT statements are executed independently
>>> (using different
>>> threads) of the DELETE.
>>>
>>> Is there

Re: Avoid locking on DELETE

[Peter Ondruška]

You would need to test various scenarios. First I would propose larger
batch size (N thousands of rows). Are you sure you execute deletes in
batches? You should have autocommit off, execute N times delete statement,
commit, repeat. Pseudo code (I am on mobile phone):

1. Acquire connection
2. Set connection autocommit to false
3. Create prepared statement with delete, DELETE FROM WHERE primary key = ?
4. Create set of primary keys to be deleted
5. Iterate set (4.) with adding those keys to delete statement (3.) as batch
6. When you reach batch size or end of key set execute batch and commit,
continue (5.)

In my case with slow disk this really performs better and should avoid your
issue as well.

Peter

On Mon, 7 Oct 2019, 22:11 Peter,  wrote:

> Hi Peter,
>
> Thanks! I have implemented this and indeed the maximum delays are lower
> but the time for a delete batch to complete takes now longer (roughly 3-4
> times; for batchSize=500, total deleted items around ~1). The problem
> is likely that I have VARCHAR for the ID column.
>
> If I increase the frequency of issuing the original DELETE statement:
>
> DELETE FROM mytable WHERE created_at < ?
>
> Won't it have a similar effect due to smaller batches?
>
> Regards
> Peter
>
> On 07.10.19 16:31, Peter Ondruška wrote:
>
> In my case I have two separate steps. First SELECT primary keys of those
> records to be deleted (in your case SELECT id FROM mytable WHERE created_at
> < some_fixed_millis). And then I issue DELETE for those primary keys in
> batches of N statements (N being configuration parameter). You could create
> stored procedure for this with two parameters (some_fixed_millis,
> batch_size).
> Your idea DELETE WHERE SELECT and limiting rows needs to be run for every
> DELETE step making unnecessary read I/O.
>
>
> On Mon, 7 Oct 2019 at 14:10, Peter  wrote:
>
>> Hi Peter,
>>
>> Thanks a lot for the suggestion.This would be nice if it performs better.
>>
>> Is the idea to split one request into smaller parts or will
>> "Select+Delete IDs" just perform better?
>>
>> And regarding the latter option - is this possible in one SQL request? So
>> something like
>>
>> DELETE FROM mytable WHERE id IN
>>
>> ( SELECT id FROM mytable WHERE created_at < some_fixed_millis OFFSET 0 ROWS 
>> FETCH NEXT 1000 ROWS ONLY )
>>
>>
>> And then loop through the results via changing OFFSET and ROWS? (Btw: the
>> column created_at is indexed)
>>
>> Or would you recommend doing this as 2 separate statements in Java/JDBC?
>> Or via maybe even just issuing the original DELETE request more frequent?
>>
>> Regards
>> Peter
>>
>> On 06.10.19 03:50, Peter Ondruška wrote:
>>
>> Peter, try this if it makes a difference:
>>
>> 1. Select entries to be deleted, note their primary keys.
>> 2. Issue delete using keys to be deleted (1.) and use short transaction
>> batches.
>>
>> On Sun, 6 Oct 2019, 01:33 Peter,  wrote:
>>
>>> Hi,
>>>
>>> I have a table "mytable" with columns "id", "created_at" and "json"
>>> (VARCHAR, BIGINT, LONG VARCHAR), where data is coming in like new 200k
>>> entries every hour and I would like to keep only entries of the last 1
>>> or 2 hours. It is expected behaviour for the user if too old entries
>>> gets lost as it is some kind of a LRU cache.
>>>
>>> The current solution is to delete entries older than 4 hours every 30
>>> minutes:
>>>
>>> DELETE FROM mytable WHERE created_at < ?
>>>
>>> I'm using this in a prepared statement where ? is "4 hours ago" in
>>> milliseconds (new DateTime().getMillis()).
>>>
>>> This works, but some (not all) INSERT statement get a bigger delay in
>>> the same order (2-5 seconds) that this DELETE takes, which is ugly.
>>> These INSERT statements are executed independently (using different
>>> threads) of the DELETE.
>>>
>>> Is there a better way? Can I somehow avoid locking the unrelated INSERT
>>> operations?
>>>
>>> What helps a bit is when I make those deletes more frequently than the
>>> delays will get smaller, but then the number of those delayed requests
>>> will increase.
>>>
>>> What also helps a bit (currently have not seen a negative impact) is
>>> increasing the page size for the Derby Network Server:
>>> -Dderby.storage.pageSize=32768
>>>
>>> Regards
>>> Peter
>>>
>>>
>>
>

Re: Avoid locking on DELETE

[Peter]

Hi Peter,

Thanks! I have implemented this and indeed the maximum delays are lower
but the time for a delete batch to complete takes now longer (roughly
3-4 times; for batchSize=500, total deleted items around ~1). The
problem is likely that I have VARCHAR for the ID column.

If I increase the frequency of issuing the original DELETE statement:

DELETE FROM mytable WHERE created_at < ?

Won't it have a similar effect due to smaller batches?

Regards
Peter

On 07.10.19 16:31, Peter Ondruška wrote:
> In my case I have two separate steps. First SELECT primary keys of
> those records to be deleted (in your case SELECT id FROM mytable WHERE
> created_at < some_fixed_millis). And then I issue DELETE for those
> primary keys in batches of N statements (N being configuration
> parameter). You could create stored procedure for this with two
> parameters (some_fixed_millis, batch_size).
> Your idea DELETE WHERE SELECT and limiting rows needs to be run for
> every DELETE step making unnecessary read I/O.
>
>
> On Mon, 7 Oct 2019 at 14:10, Peter  > wrote:
>
> Hi Peter,
>
> Thanks a lot for the suggestion.This would be nice if it performs
> better.
>
> Is the idea to split one request into smaller parts or will
> "Select+Delete IDs" just perform better?
>
> And regarding the latter option - is this possible in one SQL
> request? So something like
>
> DELETE FROM mytable WHERE id IN 
>
> ( SELECT id FROM mytable WHERE created_at < some_fixed_millis OFFSET 0 
> ROWS FETCH NEXT 1000 ROWS ONLY )
>
>
> And then loop through the results via changing OFFSET and ROWS?
> (Btw: the column created_at is indexed)
>
> Or would you recommend doing this as 2 separate statements in
> Java/JDBC? Or via maybe even just issuing the original DELETE
> request more frequent?
>
> Regards
> Peter
>
> On 06.10.19 03:50, Peter Ondruška wrote:
>> Peter, try this if it makes a difference:
>>
>> 1. Select entries to be deleted, note their primary keys.
>> 2. Issue delete using keys to be deleted (1.) and use short
>> transaction batches.
>>
>> On Sun, 6 Oct 2019, 01:33 Peter, > > wrote:
>>
>> Hi,
>>
>> I have a table "mytable" with columns "id", "created_at" and
>> "json"
>> (VARCHAR, BIGINT, LONG VARCHAR), where data is coming in like
>> new 200k
>> entries every hour and I would like to keep only entries of
>> the last 1
>> or 2 hours. It is expected behaviour for the user if too old
>> entries
>> gets lost as it is some kind of a LRU cache.
>>
>> The current solution is to delete entries older than 4 hours
>> every 30
>> minutes:
>>
>> DELETE FROM mytable WHERE created_at < ?
>>
>> I'm using this in a prepared statement where ? is "4 hours
>> ago" in
>> milliseconds (new DateTime().getMillis()).
>>
>> This works, but some (not all) INSERT statement get a bigger
>> delay in
>> the same order (2-5 seconds) that this DELETE takes, which is
>> ugly.
>> These INSERT statements are executed independently (using
>> different
>> threads) of the DELETE.
>>
>> Is there a better way? Can I somehow avoid locking the
>> unrelated INSERT
>> operations?
>>
>> What helps a bit is when I make those deletes more frequently
>> than the
>> delays will get smaller, but then the number of those delayed
>> requests
>> will increase.
>>
>> What also helps a bit (currently have not seen a negative
>> impact) is
>> increasing the page size for the Derby Network Server:
>> -Dderby.storage.pageSize=32768
>>
>> Regards
>> Peter
>>
>

Re: Avoid locking on DELETE

[Peter Ondruška]

In my case I have two separate steps. First SELECT primary keys of those
records to be deleted (in your case SELECT id FROM mytable WHERE created_at
< some_fixed_millis). And then I issue DELETE for those primary keys in
batches of N statements (N being configuration parameter). You could create
stored procedure for this with two parameters (some_fixed_millis,
batch_size).

Your idea DELETE WHERE SELECT and limiting rows needs to be run for every
DELETE step making unnecessary read I/O.


On Mon, 7 Oct 2019 at 14:10, Peter  wrote:

> Hi Peter,
>
> Thanks a lot for the suggestion.This would be nice if it performs better.
>
> Is the idea to split one request into smaller parts or will "Select+Delete
> IDs" just perform better?
>
> And regarding the latter option - is this possible in one SQL request? So
> something like
>
> DELETE FROM mytable WHERE id IN
>
> ( SELECT id FROM mytable WHERE created_at < some_fixed_millis OFFSET 0 ROWS 
> FETCH NEXT 1000 ROWS ONLY )
>
>
> And then loop through the results via changing OFFSET and ROWS? (Btw: the
> column created_at is indexed)
>
> Or would you recommend doing this as 2 separate statements in Java/JDBC?
> Or via maybe even just issuing the original DELETE request more frequent?
>
> Regards
> Peter
>
> On 06.10.19 03:50, Peter Ondruška wrote:
>
> Peter, try this if it makes a difference:
>
> 1. Select entries to be deleted, note their primary keys.
> 2. Issue delete using keys to be deleted (1.) and use short transaction
> batches.
>
> On Sun, 6 Oct 2019, 01:33 Peter,  wrote:
>
>> Hi,
>>
>> I have a table "mytable" with columns "id", "created_at" and "json"
>> (VARCHAR, BIGINT, LONG VARCHAR), where data is coming in like new 200k
>> entries every hour and I would like to keep only entries of the last 1
>> or 2 hours. It is expected behaviour for the user if too old entries
>> gets lost as it is some kind of a LRU cache.
>>
>> The current solution is to delete entries older than 4 hours every 30
>> minutes:
>>
>> DELETE FROM mytable WHERE created_at < ?
>>
>> I'm using this in a prepared statement where ? is "4 hours ago" in
>> milliseconds (new DateTime().getMillis()).
>>
>> This works, but some (not all) INSERT statement get a bigger delay in
>> the same order (2-5 seconds) that this DELETE takes, which is ugly.
>> These INSERT statements are executed independently (using different
>> threads) of the DELETE.
>>
>> Is there a better way? Can I somehow avoid locking the unrelated INSERT
>> operations?
>>
>> What helps a bit is when I make those deletes more frequently than the
>> delays will get smaller, but then the number of those delayed requests
>> will increase.
>>
>> What also helps a bit (currently have not seen a negative impact) is
>> increasing the page size for the Derby Network Server:
>> -Dderby.storage.pageSize=32768
>>
>> Regards
>> Peter
>>
>>
>

Re: Avoid locking on DELETE

[Peter]

Hi Peter,

Thanks a lot for the suggestion.This would be nice if it performs better.

Is the idea to split one request into smaller parts or will
"Select+Delete IDs" just perform better?

And regarding the latter option - is this possible in one SQL request?
So something like

DELETE FROM mytable WHERE id IN 

( SELECT id FROM mytable WHERE created_at < some_fixed_millis OFFSET 0 ROWS 
FETCH NEXT 1000 ROWS ONLY )


And then loop through the results via changing OFFSET and ROWS? (Btw:
the column created_at is indexed)

Or would you recommend doing this as 2 separate statements in Java/JDBC?
Or via maybe even just issuing the original DELETE request more frequent?

Regards
Peter

On 06.10.19 03:50, Peter Ondruška wrote:
> Peter, try this if it makes a difference:
>
> 1. Select entries to be deleted, note their primary keys.
> 2. Issue delete using keys to be deleted (1.) and use short
> transaction batches.
>
> On Sun, 6 Oct 2019, 01:33 Peter,  > wrote:
>
> Hi,
>
> I have a table "mytable" with columns "id", "created_at" and "json"
> (VARCHAR, BIGINT, LONG VARCHAR), where data is coming in like new 200k
> entries every hour and I would like to keep only entries of the last 1
> or 2 hours. It is expected behaviour for the user if too old entries
> gets lost as it is some kind of a LRU cache.
>
> The current solution is to delete entries older than 4 hours every 30
> minutes:
>
> DELETE FROM mytable WHERE created_at < ?
>
> I'm using this in a prepared statement where ? is "4 hours ago" in
> milliseconds (new DateTime().getMillis()).
>
> This works, but some (not all) INSERT statement get a bigger delay in
> the same order (2-5 seconds) that this DELETE takes, which is ugly.
> These INSERT statements are executed independently (using different
> threads) of the DELETE.
>
> Is there a better way? Can I somehow avoid locking the unrelated
> INSERT
> operations?
>
> What helps a bit is when I make those deletes more frequently than the
> delays will get smaller, but then the number of those delayed requests
> will increase.
>
> What also helps a bit (currently have not seen a negative impact) is
> increasing the page size for the Derby Network Server:
> -Dderby.storage.pageSize=32768
>
> Regards
> Peter
>

Re: Avoid locking on DELETE

[Peter Ondruška]

Peter, try this if it makes a difference:

1. Select entries to be deleted, note their primary keys.
2. Issue delete using keys to be deleted (1.) and use short transaction
batches.

On Sun, 6 Oct 2019, 01:33 Peter,  wrote:

> Hi,
>
> I have a table "mytable" with columns "id", "created_at" and "json"
> (VARCHAR, BIGINT, LONG VARCHAR), where data is coming in like new 200k
> entries every hour and I would like to keep only entries of the last 1
> or 2 hours. It is expected behaviour for the user if too old entries
> gets lost as it is some kind of a LRU cache.
>
> The current solution is to delete entries older than 4 hours every 30
> minutes:
>
> DELETE FROM mytable WHERE created_at < ?
>
> I'm using this in a prepared statement where ? is "4 hours ago" in
> milliseconds (new DateTime().getMillis()).
>
> This works, but some (not all) INSERT statement get a bigger delay in
> the same order (2-5 seconds) that this DELETE takes, which is ugly.
> These INSERT statements are executed independently (using different
> threads) of the DELETE.
>
> Is there a better way? Can I somehow avoid locking the unrelated INSERT
> operations?
>
> What helps a bit is when I make those deletes more frequently than the
> delays will get smaller, but then the number of those delayed requests
> will increase.
>
> What also helps a bit (currently have not seen a negative impact) is
> increasing the page size for the Derby Network Server:
> -Dderby.storage.pageSize=32768
>
> Regards
> Peter
>
>

Avoid locking on DELETE

[Peter]

Hi,

I have a table "mytable" with columns "id", "created_at" and "json"
(VARCHAR, BIGINT, LONG VARCHAR), where data is coming in like new 200k
entries every hour and I would like to keep only entries of the last 1
or 2 hours. It is expected behaviour for the user if too old entries
gets lost as it is some kind of a LRU cache.

The current solution is to delete entries older than 4 hours every 30
minutes:

DELETE FROM mytable WHERE created_at < ?

I'm using this in a prepared statement where ? is "4 hours ago" in
milliseconds (new DateTime().getMillis()).

This works, but some (not all) INSERT statement get a bigger delay in
the same order (2-5 seconds) that this DELETE takes, which is ugly.
These INSERT statements are executed independently (using different
threads) of the DELETE.

Is there a better way? Can I somehow avoid locking the unrelated INSERT
operations?

What helps a bit is when I make those deletes more frequently than the
delays will get smaller, but then the number of those delayed requests
will increase.

What also helps a bit (currently have not seen a negative impact) is
increasing the page size for the Derby Network Server:
-Dderby.storage.pageSize=32768

Regards
Peter