One million data reports Overview
Outline
We all know that Excel can be divided into early versions of Excel2003 (POI use of HSSF object manipulation) and Excel2007 version (using the POI XSSF operation), both of which support one million data elements are as follows:
Excel 2003: HSSF object using the POI, excel 2003 only allows the storage of up to 65,536 data, generally for less data processing amount. In this case per million level data, Excel certainly can not accommodate.
Excel 2007: When you upgrade to POI XSSF object, which can directly support excel2007 or later, because it uses ooxml format. Then excel data can support 1,048,576, a single sheet table to support nearly one million pieces of data. But there may be actual runtime also a problem, because the implementation of row objects POI reports generated, cell object, font object, they will not be destroyed, leading to the risk of OOM.
JDK performance monitoring tool introduced
No performance monitoring tool for all corollary can only stay in the theoretical stage, we can use the Java performance monitoring tools to monitor the operation of the program, including the CUP, garbage collection, memory allocation and usage, which makes the program becomes operational phase more controllable, it can also be used to prove our speculation. Here we use the Performance tool Jvisualvm JDK provided by the monitoring program run.
Jvisualvm Overview
VisualVM is Netbeans's profile subprojects have been built in JDK6.0 update 7, the ability to monitor threads, memory conditions, CPU time and memory objects in view method, GC has been the object of a reverse view stack allocation
Jvisualvm location
Jvisualvm located JAVA_HOME / bin directory, simply double-click on it to open the program. If only monitor the local java process, it does not require configuration parameters can be monitored directly open. First we need to open a Java program locally, for example I open the employee micro server process, then you can see the Java process associated with IDEA in jvisualvm interface:
Jvisualvm use
Jvisualvm simple to use, double-click on the currently running process to enter into a program of monitoring interface
Overview: You can see the start of the process parameters.
Monitoring: monitor cpu utilization, gc state, right:: top left heap utilization, memory utilization permanent area, lower left: Monitor the class, bottom right: Monitor thread
Thread: can display the name and operational status of the thread when debugging multithreaded essential, but can point to this thread into a thread view details of the operation
