When i tried to create a HTable instance in this way.
Configuration conf = HBaseConfiguration.create();
HConnection conn = HConnectionManager.getConnection(conf);
conn.getTable("TABLE_NAME");
Then i got a Exception.
#Override
public HTableInterface getTable(TableName tableName, ExecutorService pool) throws IOException {
if (managed) {
throw new IOException("The connection has to be unmanaged.");
}
return new HTable(tableName, this, pool);
}
So , i wants to know the concrete reflection of managed and 'unmanaged' Hconnection?
Before call HConnectionManager.getConnection you have to create connection using HConnectionManager.createConnection passing to it earlier created HBaseConfiguration instance. HConnectionManager.getConnection return connection which is already exists. A bit of HConnectionManager javadoc about how it handle connection pool:
This class has a static Map of HConnection instances keyed by Configuration; all invocations of getConnection(Configuration) that pass the sameConfiguration instance will be returned the sameHConnection instance
In your case, you can simply create connection using HConnectionManager.createConnection and use returned connection to open HTable
Edit:
#ifiddddddbest, I found javadocs for HConnectionImplementation which has description of managed flag(may be it will help you to understand):
#param managed If true, does not do full shutdown on close; i.e.
cleanup of connection to zk and shutdown of all services; we just
close down the resources this connection was responsible for and
decrement usage counters. It is up to the caller to do the full
cleanup. It is set when we want have connection sharing going on --
reuse of zk connection, and cached region locations, established
regionserver connections, etc. When connections are shared, we have
reference counting going on and will only do full cleanup when no more
users of an HConnectionImplementation instance.
In the newer versions of HBase(>1.0), managed flag was disappeared and all connection management now on client side,e.g. client responsible to close it and if it do this, it close all internal connections to ZK,to HBase master, etc, not only decrease reference counter.
Related
I have a small commandline utility. My code is simple I create a SingleConnectionDataSource and pass it along till it is needed and I do
ds.getConnection()
Uptil now it was working and I would get a connection and would use it but some months back this stopped working and threw an exception
Failed to obtain JDBC Connection; nested exception is java.sql.SQLException: Connection was closed in SingleConnectionDataSource. Check that user code checks should Close() before closing Connections, or set 'suppress Close' to 'true'
Now when i create the datasource I added
((SingleConnectionDataSource)db).setSuppressClose(true);
and now it works fine ( as the exception suggested)
My question is why did it stop working or how was it working before, why would it be closed even at first user. As per the java doc it is supposed to be
Implementation of SmartDataSource that wraps a single JDBC Connection
which is not closed after use.
So I should be the one closing it to begin with at the end of the process.
So technically, I have a question of why did i get the problem that i have already solved but i don't understand when did this start coming.
Edit -- It behaves like this on SQL server only and not Oracle.
Edit2 -- Sorry, In oracle it uses a different way so it works
JdbcTemplate template = new JdbcTemplate(dataSource);
So either use SuppressClose(true) or use JdbcTemplate
We would need to know your database and application server to answer definitively, but my guess is that one or the other was closing the connection after a timeout. Why are you trying to manage the connection to begin with however? Many application servers provide a connection pool.
This is a partial answer to my own question: why would it close the connection before first use?
in SingleConnectionDatasource getConnection calls
/**
* Initialize the underlying Connection via the DriverManager.
*/
public void initConnection() throws SQLException {
if (getUrl() == null) {
throw new IllegalStateException("'url' property is required for lazily initializing a Connection");
}
synchronized (this.connectionMonitor) {
closeConnection();
this.target = getConnectionFromDriver(getUsername(), getPassword());
prepareConnection(this.target);
if (logger.isDebugEnabled()) {
logger.debug("Established shared JDBC Connection: " + this.target);
}
this.connection = (isSuppressClose() ? getCloseSuppressingConnectionProxy(this.target) : this.target);
}
}
This basically, creates a closed connection to begin with. Which makes it more intriguing why did it work in the first place. This class has been with the same initConnection() method since its inception ( as far as I can see on github).
I am successful in creating a custom sampler by extending AbstractJavaSamplerClient. In the sampler implementation I am making a JMS connection and sending message to a queue. This is working great. If I configure my Thread Group to 100 with Ramp-up 1, my sampler is pushing 100 messages.
Now what I wanted to do is to make the connection only once at the JMeter startup and then reuse the same connection to send messages on each run.
Can anyone explain how to create a connection at JMeter startup and then share the same connection with the sampler.
Note: I can't use the existing JMS publisher because I want to calculate my response time based on different application event not just calculating the time taken to publish the message to JMS.
Thanks in advance.
You can use testStarted method to initialize connections for all threads. Note that this method runs once, before threads are cloned, so in testStarted you need a connection pool, which threads then can take from. For example a very primitive connection pool would be a map with some sequential ID for a key, and connection object. Each thread would take one connection from that pool, based on thread number:
So such simple pool could be initialized as:
#Override
public void testStarted()
{
int maxConnections = getThreadContext().getThreadGroup().getNumThreads();
ConcurrentMap<Integer, Object> connections = new ConcurrentHashMap<Integer, Object>();
for(int i = 0; i < maxConnections; i++)
{
Object connection = //... whatever you need to do to connect
connections.put(new Integer(i), connection);
}
// Put in the context of thread group
JMeterContextService.getContext().getVariables().putObject("MyConnections", connections);
}
(connection object could be a more specific type, based on your needs).
Later you can use it in sample method:
// Get connections pool from context
ConcurrentMap<Integer, Object> connections = (ConcurrentHashMap<Integer, Object>) JMeterContextService.getContext().getVariables().getObject("MyConnections");
// Find connection by thread ID, so each thread goes to a different connection
connections.get(getThreadContext().getThreadNum());
Here I naively assume a perfect mapping between thread number returned at run-time and initial sequential integer I used for connection initialization. Not the best assumption, could be improved, but it's a valid starting point.
You can then close and remove connection in testEnded method. This method also runs once, so we close all connections:
#Override
public void testEnded()
{
for(Entry<Integer, Object> connection : connections.entrySet())
{
connection.close(); // or do whatever you need to close it
connections.remove(connection.getKey());
}
}
Or you could just call connections.clear() when all connections are closed.
Disclosure: I did not test code in this answer directly, but used similar code fragments in the past, and reused them to answer this question. If you find any problems, feel free to update this answer.
In application start up , I am loading data source as shown below code -
#Bean(name = "dataSource")
public DataSource getDataSource() {
ComboPooledDataSource dataSource = new ComboPooledDataSource ();
dataSource.setDriverClassName("com.mysql.jdbc.Driver");
dataSource.setUrl("jdbc:mysql://localhost:3306/usersdb");
dataSource.setUsername("root");
dataSource.setPassword("secret");
return dataSource;
}
So here I would like to verify that whether the data source loaded properly,
One possible way could be datasource.getConnection() before return but here I have to create unnecessary connection object which is having some high cost.
Please help me to find a way to verify that data source has been instantiated properly. I have heard something about validate query but not sure how it would work. please suggest.
It is impossible to validate DataSource without test connection.
First of all, you define bean with singleton scope by default so single DataSource will be created with single check.
Secondly, do not worry about the creation cost of Connection because you use PooledDataSource. 'Pooled' means that pool of connections exists that is why physical connection once created can be used many times by the application.
The validate query (or test query) is used to check if existing Connection was broken. See Configuring Connection Testing for more details.
I am pretty sure that somebody else already asked this question, but I still couldn't find a satisfactory answer to it.
So, here is my scenario: I want to use the Oracle's JDBC driver implicit statement caching (documented here: http://docs.oracle.com/cd/B28359_01/java.111/b31224/stmtcach.htm#i1072607)
I need to use the connections from a 3rd party JDBC pool provider (to be more specific, Tomcat JDBC) and I have no choice there.
The problem is that the way to enable the implicit caching is a two-step process (accordingly to the documentation):
1.
Call setImplicitCachingEnabled(true) on the connection
or
Call OracleDataSource.getConnection with the ImplicitCachingEnabled
property set to true. You set ImplicitCachingEnabled by calling
OracleDataSource.setImplicitCachingEnabled(true)
2.
In addition to calling one of these methods, you also need to call
OracleConnection.setStatementCacheSize on the physical connection. The
argument you supply is the maximum number of statements in the cache.
An argument of 0 specifies no caching.
I can live with 1 (somehow I can configure my pool to use the OracleDataSource as a primary connection factory and on that I can set the OracleDataSource.setImplicitCachingEnabled(true)).
But at the second step, I already need the connection to be present in order to call the setStatementCacheSize.
My question is if there is any possibility to specify at the data source level a default value for the statementCacheSize so that I can get from the OracleDataSource connections that are already enabled for implicit caching.
PS: some related questions I found here:
Oracle jdbc driver: implicit statement cache or setPoolable(true)?
Update (possible solution):
Eventually I did this:
Created a native connection pool using oracle.jdbc.pool.OracleDataSource.
Created a tomcat JDBC connection pool using org.apache.tomcat.jdbc.pool.DataSource that uses the native one (see the property dataSource).
Enabled via AOP a poincut so that after the execution of 'execution(public java.sql.Connection oracle.jdbc.pool.OracleDataSource.getConnection())' I pickup the object and perform the setting I wanted.
The solution works great; I am just unhappy that I had to write some boilerplate to do it (I was expecting a straight-forward property).
The white paper Oracle JDBC Memory Management says that
The 11.2 drivers also add a new property to enable the Implicit Statement Cache.
oracle.jdbc.implicitStatementCacheSize
The value of the property is an
integer string, e.g. “100”. It is the initial size of the statement
cache. Setting the property to a positive value enables the Implicit
Statement Cache. The default is “0”. The property can be set as a
System property via -D or as a connection property via getConnection.
You can only change statement cache size through OracleConnection.setStatementCacheSize method.
Instead of modifying your application to call OracleConnection.setStatementCacheSize on every connection, you can create a JDBC interceptor.
#Override
public void reset(ConnectionPool pool, PooledConnection connection) {
if (connection == null) {
return;
}
Connection original = connection.getConnection();
if (!(original instanceof OracleConnection)) {
return;
}
try {
if (!((OracleConnection) original).getImplicitCachingEnabled() && implicitCachingEnabled) {
((OracleConnection) original).setImplicitCachingEnabled(implicitCachingEnabled);
log.info("Activated statement cache");
((OracleConnection) original).setStatementCacheSize(statementCacheSize);
log.info("Statement cache size set to " + statementCacheSize);
}
} catch (SQLException e) {
log.error(e.getMessage(), e);
}
}
We have our JBoss and Oracle on separate servers. The connections seem to be dropped and is causing issues with JBoss. How can I have the JBoss reconnect to Oracle if the connection is bad while we figure out why the connections are being dropped in the first place?
Whilst you can use the old "select 1 from dual" trick, the downside with this is that it issues an extra query each and every time you borrow a connection from the pool. For high volumes, this is wasteful.
JBoss provides a special connection validator which should be used for Oracle:
<valid-connection-checker-class-name>
org.jboss.resource.adapter.jdbc.vendor.OracleValidConnectionChecker
</valid-connection-checker-class-name>
This makes use of the proprietary ping() method on the Oracle JDBC Connection class, and uses the driver's underlying networking code to determine if the connection is still alive.
However, it's still wasteful to run this each and every time a connection is borrowed, so you may want to use the facility where a background thread checks the connections in the pool, and silently discards the dead ones. This is much more efficient, but means that if the connections do go dead, any attempt to use them before the background thread runs its check will fail.
See the wiki docs for how to configure the background checking (look for background-validation-millis).
There is usually a configuration option on the pool to enable a validation query to be executed on borrow. If the validation query executes successfully, the pool will return that connection. If the query does not execute successfully, the pool will create a new connection.
The JBoss Wiki documents the various attributes of the pool.
<check-valid-connection-sql>select 1 from dual</check-valid-connection-sql>
Seems like it should do the trick.
Not enough rep for a comment, so it's in a form of an answer. The 'Select 1 from dual' and skaffman's org.jboss.resource.adapter.jdbc.vendor.OracleValidConnectionChecker method are equivalent , although the connection check does provide a level of abstraction. We had to decompile the oracle jdbc drivers for a troubleshooting exercise and Oracle's internal implementation of the ping is to perform a 'Select 'x' from dual'. Natch.
JBoss provides 2 ways to Validate connection:
- Ping based AND
- Query based
You can use as per requirement. This is scheduled by separate thread as per duration defined in datasource configuration file.
<background-validation>true</background-validation> <background-validation-minutes>1</background-validation-minutes>
Some time if you are not having right oracle driver at Jboss, you may get classcast or related error and for that connection may start dropout from connection pool. You can try creating your own ConnectionValidator class by implementing org.jboss.resource.adapter.jdbc.ValidConnectionChecker interface. This interface provides only single method 'isValidConnection()' and expecting 'NULL' in return for valid connection.
Ex:
public class OracleValidConnectionChecker implements ValidConnectionChecker, Serializable {
private Method ping;
// The timeout (apparently the timeout is ignored?)
private static Object[] params = new Object[] { new Integer(5000) };
public SQLException isValidConnection(Connection c) {
try {
Integer status = (Integer) ping.invoke(c, params);
if (status.intValue() < 0) {
return new SQLException("pingDatabase failed status=" + status);
}
}
catch (Exception e) {
log.warn("Unexpected error in pingDatabase", e);
}
// OK
return null;
}
}
A little update to #skaffman's answer. In JBoss 7 you have to use "class-name" attribute when setting valid connection checker and also package is different:
<valid-connection-checker class-name="org.jboss.jca.adapters.jdbc.extensions.oracle.OracleValidConnectionChecker" />
We've recently had some floating request handling failures caused by orphaned oracle DBMS_LOCK session locks that retained indefinitely in client-side connection pool.
So here is a solution that forces session expiry in 30 minutes but doesn't affect application's operation:
<check-valid-connection-sql>select case when 30/60/24 > sysdate-LOGON_TIME then 1 else 1/0 end
from V$SESSION where AUDSID = userenv('SESSIONID')</check-valid-connection-sql>
This may involve some slow down in process of obtaining connections from pool. Make sure to test this under load.