最近准备把一千九百多万数据导入Solr中，在以前测试数据只有一两百万，全量导入没有任务问题。但是，换成一千九百万数据时，solr报内存异常(java.lang.OutOfMemoryError：GC overhead limit exceeded)，整个tomcat无法使用。我发现，我给tomcat最大堆内存512M。我觉得，可能是内存过小，于是，我把内存改大些，1024M（set JAVA_OPTS=-server -Xms1024m -Xmx1024m -XX:PermSize=128M -XX:MaxPermSize=256M ）。结果，还是内存溢出。我想已经不是tomcat内存的问题（当然，如果你的内存足够大，也是可行的）。问题，应该出在solr的dataimporthandler取数据那块。solr除了内存溢出错误，还有其他异常：

Full Import failed:java.lang.RuntimeException: java.lang.RuntimeException: org.apache.solr.handler.dataimport.DataImportHandlerException: Unable to execute query: select * from POI Processing Document # 1

at org.apache.solr.handler.dataimport.DocBuilder.execute(DocBuilder.java:278)

at org.apache.solr.handler.dataimport.DataImporter.doFullImport(DataImporter.java:411)

at org.apache.solr.handler.dataimport.DataImporter.runCmd(DataImporter.java:483)

at org.apache.solr.handler.dataimport.DataImporter$1.run(DataImporter.java:464)

Caused by: java.lang.RuntimeException: org.apache.solr.handler.dataimport.DataImportHandlerException: Unable to execute query: select * from POI Processing Document # 1

at org.apache.solr.handler.dataimport.DocBuilder.buildDocument(DocBuilder.java:418)

at org.apache.solr.handler.dataimport.DocBuilder.doFullDump(DocBuilder.java:331)

at org.apache.solr.handler.dataimport.DocBuilder.execute(DocBuilder.java:239)

... 3 more

Caused by: org.apache.solr.handler.dataimport.DataImportHandlerException: Unable to execute query: select * from POI Processing Document # 1

at org.apache.solr.handler.dataimport.DataImportHandlerException.wrapAndThrow(DataImportHandlerException.java:71)

at org.apache.solr.handler.dataimport.JdbcDataSource$ResultSetIterator.<init>(JdbcDataSource.java:281)

at org.apache.solr.handler.dataimport.JdbcDataSource.getData(JdbcDataSource.java:238)

at org.apache.solr.handler.dataimport.JdbcDataSource.getData(JdbcDataSource.java:42)

at org.apache.solr.handler.dataimport.SqlEntityProcessor.initQuery(SqlEntityProcessor.java:59)

at org.apache.solr.handler.dataimport.SqlEntityProcessor.nextRow(SqlEntityProcessor.java:73)

at org.apache.solr.handler.dataimport.EntityProcessorWrapper.nextRow(EntityProcessorWrapper.java:243)

at org.apache.solr.handler.dataimport.DocBuilder.buildDocument(DocBuilder.java:477)

at org.apache.solr.handler.dataimport.DocBuilder.buildDocument(DocBuilder.java:416)

... 5 more

Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 395,021 milliseconds ago.  The last packet sent successfully to the server was 395,021 milliseconds ago.

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)

at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)

at java.lang.reflect.Constructor.newInstance(Constructor.java:526)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)

at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074)

at com.mysql.jdbc.MysqlIO.nextRowFast(MysqlIO.java:1653)

at com.mysql.jdbc.MysqlIO.nextRow(MysqlIO.java:1409)

at com.mysql.jdbc.MysqlIO.readSingleRowSet(MysqlIO.java:2883)

at com.mysql.jdbc.MysqlIO.getResultSet(MysqlIO.java:476)

at com.mysql.jdbc.MysqlIO.readResultsForQueryOrUpdate(MysqlIO.java:2576)

at com.mysql.jdbc.MysqlIO.readAllResults(MysqlIO.java:1757)

at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2167)

at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2637)

at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2566)

at com.mysql.jdbc.StatementImpl.execute(StatementImpl.java:782)

at com.mysql.jdbc.StatementImpl.execute(StatementImpl.java:625)

at org.apache.solr.handler.dataimport.JdbcDataSource$ResultSetIterator.<init>(JdbcDataSource.java:274)

... 12 more

Caused by: java.io.EOFException: Can not read response from server. Expected to read 39 bytes, read 30 bytes before connection was unexpectedly lost.

at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2497)

at com.mysql.jdbc.MysqlIO.nextRowFast(MysqlIO.java:1634)

... 23 more

　　我搜索了一下Solr的wiki，了解到solr　jdbc取数据时，setBatchSize的问题。默认，会把很多数据放到内存中，这也是导致我的内存居高不下，后来导致内存溢出的原因。于是，我修改dataimporthandler配置文件：batchSize="-1" 解决内存溢出

　　配置文件修改如下：

　　　　　　<dataSource driver="com.mysql.jdbc.Driver" url="jdbc:mysql://localhost:3306/world" user="root"password="root" batchSize="-1" />

　　重启一个solr的core，重新导入，问题解决。