Using BufferedWriter to write is getting slower and slower, solving?

1. When extracting feature information from a large number of files (already written) and writing it to a txt target file, it is found that the first 1000 files are written faster and slower later. What is the problem?
2. The writing method I use

public static void writeText(File file, String content) {
    BufferedWriter writer = null;
    try {
        writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file, true), "UTF-8"));
        writer.append(content);
        writer.newLine();
        writer.flush();
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } finally {
        if (writer != null) {
            try {
                writer.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}
Feb.28,2021
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b36d00-2ad8a.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b36d00-2ad8a.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
Need Help?