Metacat in Ecoinfo hang
In our production version of metacat, it often hang in there and need to
restart tomcat. In that time a process of tomcat didn't response either.
But we didn't see any error message.
There are some probable issues to cause this problem
1. DB connection problem. In our code, when open a connection but we didn't
close it at end. I remember when I wrote a sript file to keep sending data to
database, There is a connection problem happend after about 1000 documents
were sent. At that time, I needed to restart tomcat and run script again.
2. Client side sent a request, but it shut down before server sending
response. This cause the problem.
3. Some thread created by metacat never be killed.
4. Unknown other reason.
Please comment it. Thanks.
#1 Updated by Jing Tao about 18 years ago
Dan tried to access same package from two instances of morpho, and made
metacat hang there.
We tired download one data package from two morpho, the first time worked but
the second time failed.
We use one morpho to download the same package 6 times and it worked fine.
Mutiple thread problem? DB connection problem?
I aked Dan to upload the package to my local machine and I will played with it.
#2 Updated by Jing Tao about 18 years ago
We upload the package and play with it couple times. But it did not cause
I decide to revise db connection code. The idea is create two another classes:
1. DBConnection, it includes Connection, index, status, age, usageCount and
warningMessage attribues. And some methods to get or set these attributes
values. This class will represent a connection object and its information.
2. DBConnectionUtil, the main attributes is "staitic DBConnection 
connectionPool". And the main methods are static getConnection,
returnConncetion, initialConncetionPool, destroyConnectionPool.
This class will be instantiated in MetacatServlet class as an static
attribute. The other class, such as DBQuery, want to use connection, just call
the static getConnection and returnConnection when it finished. So the whole
programm will share one connectionPool. (Now, we didn't do that).
The connection part in MetaCatUtil class will be removed. (I tried to keep it
on MetaCatUtil class rather than write a new class DBConnectionUtil, but
failed. It is better to create an new class).
#3 Updated by Matt Jones about 18 years ago
Sounds like a good idea. I would recommend calling the second class
DBConnectionPool rather than DBCOnnectionUtil, because it seems to represent the
Also, be sure we have fields and methods for automatically tracking the state of
each connection and the pool for debugging purposes. I think usageCount is a
#5 Updated by Jing Tao about 18 years ago
Two classes DBConnection and DBConnectionPool were added into cvs. Another
test class DBConnectionPoolTester was created too.
DBConnectionPool is a singleton class and this will make sure the whole
program share one DBConnection pool. Before a connection checking out, the
DBConnection will be checked validation (Age, connection times, and run a
simple query getMetaData). A thread will periodically running to check
connection validation and print some error or warning too. Moreover, the
thread can be configured to run or not.
Here is the test result:
10000 insert query ( insert docid into xml_documents table) and 10000 select
query were run in diferent thread. If we used MetaCatUtil to manage
connection, 6973 records were added and 136 errors ( unexpected EOF on client
connection ) were happend. The error happend means client closed the
If we use the new code, 9653 recods were added. Some failed because duplicated
key ( I used random()* 1000000 to create docid). Some I don't know why. No
error happended during running. If I killed the program, the 10 connections in
the pool were closed and caused 10 errors.
May I change the get connection and return connection for whole program? Even
there is some bugs in the new code. We need only to fix it the two classes.
And the other changes for get connection and return connection for the whole
program can still keep same.
Now in Metacat, connection sometime is class field, sometimes is method
parameter, sometime is local variable. I would like to make it all local
variable. If a method need a connection, just get it from connection pool. It
don't need be passed as class field or method parameter.
Suggestions or comments?
#6 Updated by Jing Tao about 18 years ago
A test program was applied to JDBC connection. This programm will open a
connection and used this connection to execute one insert and one select sql
command in a for loop.
But when this program connected to Oracle, it often hang there after executed
a mount of sql commands. Here is the result. ( the "# of for loop" means after
excecute the number of operation, programm hang there).
Time # of for loop
3. Couldn't run
5. Couldn't run
7. 200000 (Successfully finished all operations)
8. Couldn't run
11. Couldn't run
13. Couldn't run
14. Couldn't run
16. 1000000 (Succeefully finished all operations)
19. Couldn't run
Note: couldn't run means when start the program, it even couldn't finish one
When program hang there, there is no error message. It seem like the metacat
did. So I think this is JDBC problem cause the problem.
I will try to increase processes number in init.ora and different JDBC driver
to test it.
#7 Updated by Jing Tao about 18 years ago
When process inrcrease to 200 in init.oral file, the following is the results:
Time # of for loop Reseaon of end
1. 31053 SQL error (Unique constrain violate).
2. 137146 Shut down by me
3. 50232 Hung there
4. 187086 Shut down by me
5. 150000 Running successfully
6. 33546 Hung there
7. 100000 Running successfully
So, increase process number, the result is better.
Here is the testing result for postgresql:
Time # of for loop Reseaon of end
1. 50000 Running successfully
2. 50000 Running successfully
3. 121684 Shut down by me
Note: in time 3, I found the speed was very slow after it executed over night.
I check the number, it is about 100000. But I am not sure when it stated to
So postgresql didn't hung there, but speed is very slow after execute a mount
of sql commnad.
#8 Updated by Jing Tao about 18 years ago
The following is the result by using JDBC 9.0.1 (Process number = 50)
Time # of loop Reseaon for end
1. 36596 Hung
2. 7147 Hung
3. 5102 Hung
4. 12763 Hung
5. 6399 Hung
Though in JDBC 9.0.1 readme file, it said it resolved the bug that the JDBC
Thin driver hung in some cases during an insert. JDBC 9.0.1 still hung.
So maybe process number is the issue for hung.
#10 Updated by Jing Tao almost 18 years ago
From above testing, we know JDBC connection always hung in there after it was
used for certain amount of times (let us call this number "crital number").
Moreover, we know more process # can increase crital number.
But when process number =200, it was found that sometimes Oracle shut down by
itself. I guess current the configuration of our Oracle couldn't support
processes = 200. So I change it back to 50. Open_cursors still keeps 100 (I
monitor the v$Open_cursor table and found the open_curesor value is almost as
same as the active connection number).
My idea is: the minimum critial number is 4110 when JDBC driver is 8.1.6 and
process =50. So every DBconnection before checking out should be checked
usagecount. If usagecount is greater than 1000, it should be closed and open a
new one to replace it. So after a connection check out, it at least can be
excuted 3000 times ( 4110 -1000 = 3110) safelly. This is good for current xml
documents. But if document is too big, we still take the risk of hung for
inserting it into xml_nodes and xml_index tables. But the possibility of hung
is not high ( From testing, lots of connection can be excetued more than
Our new code was tested. The package which we used to test is Jornada, it is
big. As drescribed before, if two morphos upload this package to metacat at
same time and sometimes will cause hung problem. New code was tested by two
morpho uploading this package at same time for more than 60 times, hung
problem never happened! Dan and I tried to upload this package from three
morphos at same time for two times, it worked good too.
I think this problem was fixed in some level and do we need to install it in
ecoinfo to see what will happen?