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Sample of exponential backoff on a set with Couchbase Server
package com.couchbase.sample.dataloader;
import com.couchbase.client.CouchbaseClient;
import java.io.IOException;
import java.net.URI;
import java.util.List;
import net.spy.memcached.internal.OperationFuture;
import net.spy.memcached.ops.OperationStatus;
/**
*
* The StoreHandler exists mainly to abstract the need to store things
* to the Couchbase Cluster even in environments where we may receive
* temporary failures.
*
* @author ingenthr
*/
public class StoreHandler {
CouchbaseClient cbc;
private final List<URI> baselist;
private final String bucketname;
private final String password;
/**
*
* Create a new StoreHandler. This will not be ready until it's initialized
* with the init() call.
*
* @param baselist
* @param bucketname
* @param password
*/
public StoreHandler(List<URI> baselist, String bucketname, String password) {
this.baselist = baselist; // TODO: maybe copy this?
this.bucketname = bucketname;
this.password = password;
}
/**
* Initialize this StoreHandler.
*
* This will build the connections for the StoreHandler and prepare it
* for use. Initialization is separated from creation to ensure we would
* not throw exceptions from the constructor.
*
*
* @return StoreHandler
* @throws IOException
*/
public StoreHandler init() throws IOException {
// I prefer to avoid exceptions from constructors, a legacy we're kind
// of stuck with, so wrapped here
cbc = new CouchbaseClient(baselist, bucketname, password);
return this;
}
/**
*
* Perform a regular, asynchronous set.
*
* @param key
* @param exp
* @param value
* @return the OperationFuture<Boolean> that wraps this set operation
*/
public OperationFuture<Boolean> set(String key, int exp, Object value) {
return cbc.set(key, exp, cbc);
}
/**
* Continuously try a set with exponential backoff until number of tries or
* successful. The exponential backoff will wait a maximum of 1 second, or
* whatever
*
* @param key
* @param exp
* @param value
* @param tries number of tries before giving up
* @return the OperationFuture<Boolean> that wraps this set operation
*/
public OperationFuture<Boolean> contSet(String key, int exp, Object value,
int tries) {
OperationFuture<Boolean> result = null;
OperationStatus status;
int backoffexp = 0;
try {
do {
if (backoffexp > tries) {
throw new RuntimeException("Could not perform a set after "
+ tries + " tries.");
}
result = cbc.set(key, exp, value);
status = result.getStatus(); // blocking call, improve if needed
if (status.isSuccess()) {
break;
}
if (backoffexp > 0) {
double backoffMillis = Math.pow(2, backoffexp);
backoffMillis = Math.min(1000, backoffMillis); // 1 sec max
Thread.sleep((int) backoffMillis);
System.err.println("Backing off, tries so far: " + backoffexp);
}
backoffexp++;
if (!status.isSuccess()) {
System.err.println("Failed with status: " + status.getMessage());
}
} while (status.getMessage().equals("Temporary failure"));
} catch (InterruptedException ex) {
System.err.println("Interrupted while trying to set. Exception:"
+ ex.getMessage());
}
if (result == null) {
throw new RuntimeException("Could not carry out operation."); // rare
}
// note that other failure cases fall through. status.isSuccess() can be
// checked for success or failure or the message can be retrieved.
return result;
}
}
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