In python when you open a file using open command the your can read the content of the file. read will read the whole content of the file at once, while readline reads the content of the file line by line.

NOTE: if file is huge, read() is definitely a bad idea, as it loads (without size parameter), whole file into memory.

NOTE: it is good practice to use the with keyword when dealing with file objects. The advantage is that the file is properly closed after its suite finishes, even if an exception is raised at some point. (We have reviewed with in depth a couple days ago)

NOTE: read function gets a size parameter that specifies the chunks read from a file. If the end of the file has been reached, f.read() will return an empty string.

For reading lines from a file, you can loop over the file object. This is memory efficient, fast, and leads to simple code:

>>>
 >>> for line in f:
 ...     print(line, end='')
 ...
 This is the first line of the file.
 Second line of the file

#python #file #read #readline #efficiency

MongoDB has a top utility like top linux command that displays how much time spent on read, write and total on every name space (collection).


To run mongotop you just need to run:

mongotop

The output is something like below:

root@hs-1:~# mongotop
 2018-01-09T13:42:42.177+0000    connected to: 127.0.0.1

                     ns           total    read    write    2018-01-09T13:42:43Z
                 users.profile     28ms    28ms      0ms
               authz.tokens        7ms     7ms      0ms
                mielin.obx         3ms     3ms      0ms
              conduc.contacts      1ms     1ms      0ms
           admin.system.roles      0ms     0ms      0ms

The above query will run every second, to increase the interval use mongotop YOUR_INTERVAL_INSECOND.

If you want the result in json use mongotop --json.

If you want to return the result once and exit use mongotop --row-count

#mongodb #mongo #mongotop #read #write

See live disk IO status by using iostat:

iostat -dx 1

The output has many columns. The part I'm interested in for now is r/s which refers to read per second and w/s which is write per
second. To see size per second in read and write see columns rkB/s, wkB/s in their corresponding order.

NOTE: if you don't have iostat on your linux os install it on debian by issuing apt-get install sysstat command.


#linux #debian #iostat #read_per_second #write_per_second #sysstat

Elasticsearch gives below error:

Config: Error 403 Forbidden: blocked by: [FORBIDDEN/12/index read-only / allow delete (api)];: [cluster_block_exception] blocked by:   [FORBIDDEN/12/index read-only / allow delete (api)];

This error may happen when server storage is totally full and elasticsearch puts your indexes in read only mode. If you have enough
space now and are sure there is no other matter for elasticsearch and it behaves normally, remove read only mode from index block:

curl -XPUT -H "Content-Type: application/json" http://localhost:9200/.monitoring-*/_settings -d '{"index.blocks.                       read_only_allow_delete": null}'

#elasticsearch #read_only #index #cluster_block_exception