Databases
StackOverflow2013
Postsdbo
POIs C3P0 thread-safe?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POIs C3P0 thread-safe?
    primarykey
    data
    text
    <p>An interruption exception (java.lang.InterruptedException) occurs as I'm trying to perform some simple read (SELECT) operations using C3P0 on a MySQL database. The exception occurs as I increase the number of parallel threads more than 100 (I have tried with 5,10,20,60 and 100). The statement I execute is as simple as :</p> <pre><code>SELECT `Model.id` FROM `Model` LIMIT 100; </code></pre> <p>My connections are pooled from a ComboPooledDataSource which is configured using the following properties (see also the <a href="http://www.mchange.com/projects/c3p0/index.html" rel="noreferrer">C3P0 manual</a>):</p> <pre><code>c3p0.jdbcUrl=jdbc:mysql... c3p0.debugUnreturnedConnectionStackTraces=true c3p0.maxIdleTime=5 c3p0.maxPoolSize=1000 c3p0.minPoolSize=5 c3p0.initialPoolSize=5 c3p0.acquireIncrement=3 c3p0.acquireRetryAttempts=50 c3p0.numHelperThreads=20 c3p0.checkoutTimeout=0 c3p0.testConnectionOnCheckin=true c3p0.testConnectionOnCheckout=true user=*** password=*** </code></pre> <p>The MySQL server on the machine I run the tests is configured to accept 1024 connections and the unit tests I run are successfully executed (the data are retrieved from the database as expected). However, in the C3P0 log file, I find the following warning:</p> <pre><code>15:36:11,449 WARN BasicResourcePool:1876 - com.mchange.v2.resourcepool.BasicResourcePool@9ba6076 -- Thread unexpectedly interrupted while performing an acquisition attempt. java.lang.InterruptedException: sleep interrupted at java.lang.Thread.sleep(Native Method) at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1805) at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547) </code></pre> <p>I'd like to know the reason for that warning and second its possible impact on the software's robustness and stability. Note that after use, I close the result set, the SQL statement and the connection. Finally, once the test is over, I close the pool by calling the method <code>ComboPooledDataSource#close()</code>. What is more weird (and seems to be to reveal a synchronization problem), is that if I give enough time to the pool using the following...</p> <pre><code>Thread.sleep(10000); // wait for some time datasource.close(); </code></pre> <p>No warnings will appear in the logs! Dο you think this raises a thread safety issue for C3P0 or am I doing something the wrong way?</p> <p><strong>Update 1:</strong></p> <p>Let me mention that removing the <code>Thread.sleep(10000)</code>, apart from what already mention, causes the following info to be logged in the MySQL log file:</p> <pre><code>110221 14:57:13 [Warning] Aborted connection 9762 to db: 'myDatabase' user: 'root' host: 'localhost' (Got an error reading communication packets) </code></pre> <p>Might shed some more light...</p> <p>Update 2:</p> <p>Here is my MySQL server configuration. The number of maximum allowed connections by server is set to 1024 (as I mentioned above) which is adequate for what I'm trying to do. </p> <pre><code>[mysqld] max_allowed_packet = 64M thread_concurrency = 8 thread_cache_size = 8 thread_stack = 192K query_cache_size = 0 query_cache_type = 0 max_connections = 1024 back_log = 50 innodb_thread_concurrency = 6 innodb_lock_wait_timeout = 120 log_warnings </code></pre> <p>To obfuscate any doubt, I verified that the maximum number of connections is properly set by:</p> <pre><code>show global variables where Variable_name='max_connections'; +-----------------+-------+ | Variable_name | Value | +-----------------+-------+ | max_connections | 1024 | +-----------------+-------+ 1 row in set (0.00 sec) </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USPantelis Sopasakis
    1. USPantelis Sopasakis
    plurals
    1. This table or related slice is empty.
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POIs C3P0 thread-safe?
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POIs C3P0 thread-safe?
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POIs C3P0 thread-safe?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COThis is not the droid you're looking for.
      singulars
      1. POIs C3P0 thread-safe?
      1. USPaul Tomblin
    2. COUse the source, Pantelis. [okay, that's enough Star Wars references - can someone help this guy?]
      singulars
      1. POIs C3P0 thread-safe?
      1. USSpacedman
    3. COI might be wrong here, but are you really supposed to close the connection? I'm not quite sure. Anyway, what probably happens is that C3PO worker threads are simply waiting for new requests to process for some time after the last one, then die. If you close the connection before that time, they are interrupted and die. (And produce this stack trace, which usually doesn't indicate an error.) If you wait for 30 seconds, they all die of natural causes and you don't get the stack trace.
      singulars
      1. POIs C3P0 thread-safe?
      1. USbiziclop
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload