Java neo4j，REST和内存 [英] Java neo4j, REST and memory
问题描述
我在Jersey tomcat下使用neo4j java嵌入式版本为REST API部署了一个应用程序。
通过使用jconsole测量内存使用情况，我注意到每个REST调用都添加了200Mb的内存（我认为这是因为整个图形被加载到内存中）。因此，只需5次调用，服务器就会分配1Gb的内存，这很多！要清理内存，我必须等待垃圾收集器（阈值设置为1Gb）。
I've deployed an app using neo4j java embedded version under Jersey tomcat for REST API. By measuring memory usage with jconsole I noticed each REST call adds 200Mb of memory (which I think it's because the entire graph gets loaded into memory). Therefore with just 5 calls, server allocates 1Gb of memory, which is a lot! To clean up memory I have to wait garbage collector (threshold set to 1Gb).
这是正常的行为，因为我使用的是neo4j java嵌入式版本，或者我是做一些非常错误的事情？当API调用结束时，我应该做些什么来释放内存？
Is it a normal behavior because I'm using the neo4j java embedded version or am I doing something terribly wrong? What I'm supposed to do to free memory when the API call ends?
这里示例代码：
@GET
@Produces(MediaType.APPLICATION_JSON + ";charset=utf-8")
public Response getApi( @QueryParam("q") String query){
try{
// new neo instance here with EmbeddedGraphDatabase
... some code
// stop neo
}catch(Exception ex){
// stop neo
}
return response.ok("json data here").build();
}
谢谢，
Daniele
Thanks, Daniele
--------完整的课程代码----------
-------- COMPLETE CLASS CODE ----------
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.QueryParam;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import org.neo4j.graphdb.GraphDatabaseService;
import org.neo4j.kernel.EmbeddedGraphDatabase;
@Path("/API")
public class API {
@GET
@Produces(MediaType.APPLICATION_JSON)
public Response apiCall(@QueryParam("q") String query){
GraphDatabaseService graphDb;
try{
// start neo
graphDb = new EmbeddedGraphDatabase( "/var/neo4jdb/" );
this.registerShutdownHook( graphDb );
// API + NEO code here..
// stop neo
graphDb.shutdown();
}catch(Exception ex){
// stop neo
graphDb.shutdown();
}
Response response = null;
return response.ok("This is your query: "+query).build();
}
/**
* Server shutdown
*/
public void registerShutdownHook( final GraphDatabaseService graphDb ){
// Registers a shutdown hook for the Neo4j instance so that it
// shuts down nicely when the VM exits (even if you "Ctrl-C" the
// running example before it's completed)
Runtime.getRuntime()
.addShutdownHook( new Thread()
{
@Override
public void run()
{
graphDb.shutdown();
}
} );
}
}
然后我调用REST服务通过这样的浏览器 http：// localhost：8080 / API？q = test
And then I call the REST service via browser like this http://localhost:8080/API?q=test
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.QueryParam;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import org.neo4j.graphdb.GraphDatabaseService;
import org.neo4j.kernel.EmbeddedGraphDatabase;
@Path("/API")
public class API {
@GET
@Produces(MediaType.APPLICATION_JSON)
public Response apiCall(@QueryParam("q") String query){
GraphDatabaseService graphDb;
try{
// start neo
Neo4jSingleton neo4jInstance = new Neo4jSingleton();
GraphDatabaseService graphDb = null;
graphDb = neo4jInstance.getInstance(DB_PATH);
this.registerShutdownHook( graphDb );
// API + NEO code here..
// cypher query
ExecutionEngine engine = new ExecutionEngine(graphDb);
String queryString = "Cypher query code";
ExecutionResult result = engine.execute( queryString );
// fetch results here..
// never stop neo now with singleton
}catch(Exception ex){
// stop neo
graphDb.shutdown();
}
Response response = null;
return response.ok("This is your query: "+query).build();
}
/**
* Server shutdown
*/
public void registerShutdownHook( final GraphDatabaseService graphDb ){
// Registers a shutdown hook for the Neo4j instance so that it
// shuts down nicely when the VM exits (even if you "Ctrl-C" the
// running example before it's completed)
Runtime.getRuntime()
.addShutdownHook( new Thread()
{
@Override
public void run()
{
graphDb.shutdown();
}
} );
}
}
public class Neo4jSingleton {
private static GraphDatabaseService db;
public Neo4jSingleton() {
}
/*
* il metodo di restituire un'unica istanza
* contenente il database neo4j
*/
public static GraphDatabaseService getInstance(String DB_PATH)
{
//Boolean isDbChange=verifyDbChange();
if (db == null /*|| isDbChange*/)
{
db = new EmbeddedGraphDatabase(DB_PATH);
}
return db;
}
}
推荐答案
你不得为每个请求创建Neo4j实例。请创建一次，然后将其传入，或者在静态字段中进行hacky（因为您为每个请求重新创建资源实例），或者在Neo4j服务器中使用注入 @Context的Provider 。
You must not create Neo4j instance for every request. Please create it just once and then pass it in, either hacky in a static field (as you're resource instance is recreate for each request) or as in Neo4j server with an Provider which is injected with @Context.
关于内存使用情况。 Neo4j根据您的使用情况构建内部缓存，以便下次更快地提供相同的查询。这可能相当于一些已用的内存。
Regarding memory usage. Neo4j builds up internal caches according to your usage to serve the same queries faster the next time. So that might amount for some of the used memory.
Btw。你的图表有多大，你做的典型操作是什么？
Btw. how large is your graph and what are the typical operations you do?
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