Java Platform, Standard Edition Troubleshooting Guide
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4.5 I/O Performance

When a Java Application spends a lot of time either in Socket Read, Socket Write, File Read or File Write, then I/O or networking may be the bottleneck. To diagnose I/O issues in applications, take a look at Socket Read tab under the I/O group, as shown in Figure 4-5.

Figure 4-5 shows that the application had 100 reads from the remote address The total number of bytes read is 356 bytes and the total time spent waiting is 1 min 57 s. Select By Event tab at the left top corner and look at each event to analyze the time spent and data read.

File or networking I/O issues are diagnosed in a similar fashion. Look at the files read to or written to the most, then see each file read/write and time spent on I/O.

All the tabs in I/O by default list events with a duration longer than 20 ms. When starting a flight recording, you can lower the File I/O Threshold or the Socket I/O Threshold to gather more data, potentially with a higher performance impact.

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