查询DBpedia时重复503的消息 [英] Repeating 503's messages when querying DBpedia

问题描述

我正在对DBpedia SPARQL端点进行一系列查询（从循环内部）。代码看起来或多或少是这样的：

I'm conducting a series of queries to DBpedia SPARQL endpoint (from inside a loop). The code looks more or less like this:

for (String citySplit : citiesSplit) {
  RepositoryConnection conn = dbpediaEndpoint.getConnection();
  String sparqlQueryLat = " SELECT ?lat ?lon WHERE { "
                        + "<http://dbpedia.org/resource/" + citySplit.trim().replaceAll(" ", "_") + "> <http://www.w3.org/2003/01/geo/wgs84_pos#lat> ?lat . "
                        + "<http://dbpedia.org/resource/" + citySplit.trim().replaceAll(" ", "_") + "> <http://www.w3.org/2003/01/geo/wgs84_pos#long> ?lon ."
                        + "}";
  TupleQuery queryLat = conn.prepareTupleQuery(QueryLanguage.SPARQL, sparqlQueryLat);
  TupleQueryResult resultLat = queryLat.evaluate();
}    

问题是，经过几次迭代，我得到了一条503消息：

The problem is that, after a few iterations, I get a 503 message:

httpclient.wire.header - << "HTTP/1.1 503 Service Temporarily Unavailable[\r][\n]"
(...)
org.openrdf.query.QueryInterruptedException
    at org.openrdf.http.client.HTTPClient.getTupleQueryResult(HTTPClient.java:1041)
    at org.openrdf.http.client.HTTPClient.sendTupleQuery(HTTPClient.java:438)
    at org.openrdf.http.client.HTTPClient.sendTupleQuery(HTTPClient.java:413)
    at org.openrdf.repository.http.HTTPTupleQuery.evaluate(HTTPTupleQuery.java:41)

如果我理解正确，则此503消息来自DBpedia。我对吗？
成功执行的连续查询数是可变的。有时，它会在获取消息之前运行13秒钟，有时需要15分钟。
无论如何，我认为这是不正常的。
可能会发生什么？

If I understand correctly, this 503 message is from DBpedia. Am I right? The number of consecutive queries that manage to succeed is variable. Sometimes it runs for 13 seconds before getting the message, sometimes 15 minutes. In any case, I don't think this is normal. What could be happening?

推荐答案

通过DBpedia Wiki的Web 页面访问DBpedia数据集，该页面在 1.1。公用SPARQL端点说：

The Accessing the DBpedia Data Set over the Web page of the DBpedia wiki says, in section 1.1. Public SPARQL Endpoint says:

公平使用政策：请阅读这篇文章了解有关公共DBpedia端点限制的信息。这些可能也很有用[sic]： 1 ， 2 。

Fair Use Policy: Please read this post for information about restrictions on the public DBpedia endpoint. These might also be usefull [sic]: 1, 2.

链接的帖子说，公共DBpedia SPARQL端点实现了速率限制。

The linked post says that the public DBpedia SPARQL endpoint implements rate limiting.

http://dbpedia.org/sparql 端点同时对您可以建立的连接数/秒进行速率限制，并对结果集和查询时间进行限制，因为根据以下设置：

The http://dbpedia.org/sparql endpoint has both rate limiting on the number of connections/sec you can make, as well as restrictions on resultset and query time, as per the following settings:

[SPARQL]
ResultSetMaxRows           = 2000
MaxQueryExecutionTime      = 120
MaxQueryCostEstimationTime = 1500

这些都是为了确保每个人都有平等的机会去引用数据来自dbpedia.org，以及防范写得不好的查询/机器人。

These are in place to make sure that everyone has a equal chance to de-reference data from dbpedia.org, as well as to guard against badly written queries/robots.

我认为您很可能达到了该限制。

I think that it is likely that you are hitting that limit.

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