com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
Posted by: ma haibo
Date: March 03, 2008 09:08PM

most of the time connection works ok.
somtime we are getting

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
Last packet sent to the server was 119977 ms ago.

I use mysql 5.0.27.
The server have 4G memory.
in my.cnf:
port = 3306
socket = /tmp/mysql.sock
key_buffer = 384M
max_allowed_packet = 10M
table_cache = 512
sort_buffer_size = 1024M
read_buffer_size = 1024M
join_buffer_size = 2000M
key_buffer_size = 1024M
read_rnd_buffer_size = 8M
myisam_sort_buffer_size = 1024M
thread_cache_size = 8
query_cache_size = 32M
# Try number of CPU's*2 for thread_concurrency
thread_concurrency = 8

innodb_additional_mem_pool_size = 64M
innodb_autoextend_increment = 256M

innodb_buffer_pool_size = 2096M # 50% ~ 80% of system memory
innodb_additional_mem_pool_size = 64M

java code :
public synchronized static DataSource createDataSource(String driver,String url,String username,String password) throws SQLException, ClassNotFoundException {


DataSource ds_unpooled = DataSources.unpooledDataSource(url,username,password);

Map overrides = new HashMap();

overrides.put("acquireIncrement", 2);
overrides.put("minPoolSize", 15);
overrides.put("maxPoolSize", 30);

overrides.put("maxStatements", 10000);

overrides.put("maxIdleTime", 3600 );

overrides.put("automaticTestTable", "C3P0TestTable");
overrides.put("testConnectionOnCheckin", true);

overrides.put("testConnectionOnCheckout", true);

// create the PooledDataSource using the default configuration and our overrides
DataSource ds_pooled = DataSources.pooledDataSource( ds_unpooled, overrides );
return ds_pooled;

Any help will be greatly appreciated!thank you!

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com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
March 03, 2008 09:08PM

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