Using smallfiles this runtime option can reduce the journal file size to 128M.įirst of all, we must know that in this principle, there are two files and two views. Generally, there are only 2~3 journal files in the folder where the journal file is located, unless you use mongodb to write a large amount of data every second. Once a journal file records the write operation If all have been used, mongodb will delete this journal file.
Mongodb journaly full#
If a journal file is full of 1G in size, mongodb will create a new journal file to use. The journal file is named at the beginning of "j._" and is append only. The lower the value, the higher the refresh output frequency and the higher the data security, but the higher the overhead on disk performance. However, this millisecond value can be modified. share it.īy default, mongodb flushes data in the journal file every 100 milliseconds, but this is when the data file and the journal file are on the same disk volume, and if the data file and the journal file are not on the same disk volume, the default refresh output time It is 30 milliseconds. I hope that if someone does this experiment, I will share the process. Unfortunately, when I tried to do this experiment, I tried several times to convert the ext3 file system on the virtual machine CentOS to ext4 without success, so I finally gave up this experiment. In addition, I have seen people on the Internet that if the ext4 file system is used, the pre-allocation time will be reduced a lot (it is said that the performance improvement of ext4 based on ext3 is much higher than the performance improvement of ext3 based on ext2. This pre-allocated file does not contain data, so this is the operation The way is safe. If you want to avoid this pre-allocation action, you can copy a pre-allocated file from another mongodb instance and put it in your journal path. This process will take a long time (so in the teacher’s video demonstration), It took a long time to start the service for the first time), the service is unavailable during this time.
At this time, mongodb will now allocate disk space for the journal file on the disk. Please use -journal if you want durability.", So I need to bring the -journal parameter when starting mongodb and if you don't want to start the journal on the machine that starts the journal by default, you can bring the -nojournal parameter.īefore starting the service with journal enabled for the first time, there is usually no journal file on the disk. So on my 32-bit machine with version 2.4.3 installed, every time I start mongodb, it prompts "warning: 32-bit servers don't have journaling enabled by default. On a 64-bit machine, the journal is turned on by default for versions above 2.0, but on a 32-bit machine, or for versions below 2.0, the journal is not turned on by default.
The role of journal files in MongoDB is equivalent to the role of redo log files in oracle, which can repeat database operations even if the server is down unexpectedly.
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