Hi Jay,One issue which you may be seeing is that Derby incurs a noticeable burp the first time that you compile a given SQL statement. If you use ? parameters, then you will not see that burp the second time you try to run that statement text. This is because Derby uses the statement text as a hash key to look up previously compiled execution plans. For more information, please see the section titled "Use prepared statements with substitution parameters" in the Derby Tuning Guide: http://db.apache.org/derby/docs/10.4/tuning/
Try the following instead and let us know what kind of spike you see on your second and later deletes:
PreparedStatement ps = connection.prepareStatement( "delete from attendance_info where child_id = ?" );
ps.setInt( 1, 2 ); int result = ps.executeUpdate(); Regards, -Rick Iwud H8u wrote:
Rick Hillegas-2 wrote:Hi Jay,You may be able to get the behavior you want by adding a DELETE trigger to child_info or to progeny. The trigger would fire a Java PROCEDURE to keep your tables in sync. For more information, please see the "CREATE TRIGGER statement" section of the Reference Guide. Alternatively, if the orphaned parent_info rows are harmless cruft, you might get away with garbage-collecting them lazily when your application is idle.Yes, I was thinking of going the way of the triggers if the on delete cascade behaviour doesnt not improve. Hopefully that should get rid of my little problem. The ON DELETE cascade seemed like a much more straightforward way of doing it. Also I never experienced this issue with HSQLDB which I was using before I migrated to Derby. I migrated because Derby offers encryption out of the box unlike HSQLDB ... :) See below for why I am pointing fingers at Derby ...It sounds as though you have embedded Derby inside a sophisticated UI. Why do you think the memory/cpu burp is in Derby rather than somewhere else in your application?I am still hoping that someone might answer my original memory usage/computational overhead question on row deletion.... Do you have any ideas about that?Yes, I have tried to create a rich client (using some ideas from the filthy java clients book) but then I am pretty sure my UI is not to blame because I profile the app resource usage regularly. Also here is a debugging script which just runs a delete statement ... (script below). The time for this little script to execute is 6000ms (6 sec) which for a UI isn't acceptable. Also it spikes the CPU usage to 100% for a little while and freezes up the app (ultimately causing an OOM exception). logger.debug("Before calling create statement"); long before = Calendar.getInstance().getTimeInMillis(); Statement st = connection.createStatement(); logger.debug("statement created"); int result = st.executeUpdate("DELETE FROM ATTENDANCE_INFO WHERE CHILD_ID = "+2); long after = Calendar.getInstance().getTimeInMillis(); logger.debug("Query time = "+(after-before)); I run this bit of code from a simple test class and the memory spikes from40MB to 100-120MB just as after it creates the statement ...Rick Hillegas-2 wrote:Iwud H8u wrote:Hi Rick, That is a good suggestion. I had originally envisaged a new row for each child in the parent_info table. Your schema suggestion looks good expect, when deleting a child record, I will now have to delete the parent from parent_info after checking no other child has the same parent!Hi Jay,You may be able to get the behavior you want by adding a DELETE trigger to child_info or to progeny. The trigger would fire a Java PROCEDURE to keep your tables in sync. For more information, please see the "CREATE TRIGGER statement" section of the Reference Guide. Alternatively, if the orphaned parent_info rows are harmless cruft, you might get away with garbage-collecting them lazily when your application is idle.It sounds as though you have embedded Derby inside a sophisticated UI. Why do you think the memory/cpu burp is in Derby rather than somewhere else in your application?I am still hoping that someone might answer my original memory usage/computational overhead question on row deletion.... Do you have any ideas about that?Regards, -RickThanks, Jay Rick Hillegas-2 wrote:Hi Jay, I have a couple comments about your schema:1) You don't need to create ChildIdIndex. This is because Derby creates backing indexes for UNIQUE, PRIMARY KEY, and FOREIGN KEY constraints. For more information, please see the section titled "CONSTRAINT clause" in the Derby Reference Guide: http://db.apache.org/derby/docs/10.4/ref/2) I am puzzled by the relationship between child_info and parent_info. Do you really intend a parent to have only one child? Or have you denormalized the parent_info table so that each parent has multiple rows in parent_info, one for each of their children? You may want to consider normalizing this schema as follows:a) remove the child_id column from parent_infob) create an additional table to model the many-to-many relationship between parents and children:create table progeny (parent_id int not null foreign key references parent_info( parent_id ) on delete cascade, child_id int not null foreign key references child_info( child_id ) on delete cascade) Hope this helps, -Rick Iwud H8u wrote:Michael Segel wrote:Since you're a bit cryptic.. Hmm sorry I wasn't intending to be cryptic ... was trying not to beverbose!You are right about the column IDs ... lemme post the actual SQL statements for creating the tables themselves... nothing confidential in them I guess.... :) ==================== tables ========================== CREATE TABLE Child_info (child_id INTEGER NOT NULL PRIMARY KEY GENERATEDALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1) , first_name VARCHAR(32) NOT NULL, middle_name VARCHAR(32) NOT NULL, last_name VARCHAR(32) NOT NULL)CREATE TABLE parent_info (parent_id INTEGER NOT NULL PRIMARY KEY GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1) , " + "first_name VARCHAR(32) NOT NULL, middle_name VARCHAR(32) DEFAULT ' ', " + "last_name VARCHAR(32) NOT NULL, child_id INTEGER NOT NULL , FOREIGN KEY(child_id) REFERENCES Child_info (child_id) ON DELETE CASCADE) CREATE TABLE attendance_info (attendance_id INTEGER NOT NULL PRIMARY KEYGENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1) , monday VARCHAR(16),tuesday VARCHAR(16), wednesday VARCHAR(16) , thursday VARCHAR(16) , friday VARCHAR(16) ,UNIQUE (child_id) , FOREIGN KEY(monday) REFERENCES sessions (session_name) ON DELETE CASCADE, FOREIGN KEY(tuesday) REFERENCES sessions(session_name) ON DELETE CASCADE, FOREIGN KEY(wednesday) REFERENCESsessions (session_name) ON DELETE CASCADE, FOREIGN KEY(thursday) REFERENCES sessions (session_name) ON DELETE CASCADE, FOREIGN KEY(friday) REFERENCES sessions (session_name) ON DELETE CASCADE, FOREIGN KEY(room_name) REFERENCES rooms (room_name) ON DELETE CASCADE, FOREIGN KEY(child_id) REFERENCES Child_info(child_id) ON DELETE CASCADE ) As you can see the lines in bold declare the primary key and foreign keys(with on delete cascade).I am guessing child_id does not need a separate index to be generated because it is the primary key in Child_info table and atttendance_info tables. However child_id cant be either unique or primary in parent_info table because there will be atleast two parents with the same child_id.I however created and index on this table usingCREATE INDEX ChildIdIndex ON PARENT_INFO(CHILD_ID)My query times for something likeDELETE FROM CHILD_INFO WHERE CHILD_ID = 1 is around 6 seconds with only two row entries CHILD_INFO, 6 row entries in PARENT_INFO and just one entry in ATTENDANCE_INFO!Hope this makes sense...On Table A, you show Col_x_ID, but in your foreign key, you show Col_x. I'm going to assume that you meant Col_x_ID.On Table A, do you have an index on Col_x_ID? Is Col_x_ID a unique ID? If so, is this the primary key for the table?That would be the first thing to look at. If no index exists, my guess would be that you're doing a sequential table scan.HTH-Mike_____ From: jay _ [mailto:[EMAIL PROTECTED] Sent: Monday, August 18, 2008 4:16 AMTo: derby-user@db.apache.org Subject: memory usage for row delete cascadeHi all, I have a database with three tables (Table_A, Table_B and Table_C). There is one identity column in Table_A which acts as a foreign key in Tables B and C with an ON DELETE CASCADE.Here is the table structure .... Table A : Col_x_ID , Coly_Name, .... Table B : Col_p_ID, Col_q_Name, .... Col_x ... FOREIGN KEY(Col_x)REFERENCES Table A (Col_x) ON DELETE CASCADE) Table B : Col_m_ID, Col_n_Name, .... Col_x ... FOREIGN KEY(Col_x) REFERENCES Table A (Col_x) ON DELETE CASCADE) When I now try to delete a row in Table_A, I experience a spike in CPU usage to almost 100% and also the memory usage bumps from 40MB to 100MB. This remains sustained for a few seconds (like 5 seconds) causing the UI to almost freeze in my application. Even worse, it causes an Out of Memory Exception! I am pretty sure that something isn't quite right with what I am experiencing. I know row inserts and deletes are computationally expensive,but surely it has to be less expensive than what I am experiencing.I'd appreciate if anyone can tell me how to optimise this or is there a more efficient method to delete entries with a cascade effect? I am running Derby version 10.4.1.3 on MacOSX with JRE 1.5 version 6. Thanks, Jay_____Get thousands of games on your PC, your mobile phone, and the web with WindowsR. Game with <http://clk.atdmt.com/MRT/go/108588800/direct/01/> Windows
