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Lazy Admin’s Guide To Changing Mongo Oplog Size

December 4, 2014

Have you read Mongo’s official guide to changing the size of your oplog and found it a bit intimidating? Are you resizing it because you already have replication problems anyway? Might as well rebuild your secondary and increase the oplog size in one shot. It’s basically the same as the procedure outlined here:

1. Set the oplog size in /etc/mongodb.conf. Just add this line (the size is in MB):
oplogSize = 102400

2. Stop your server with:

3. Empty the data directory – the one set by dbPath. You can remove all the files but it’s probably a better idea to move them to a backup directory in case anything goes wrong.

4. Start your server.

That’s it. The server will find the empty data directory, initialize it using the new oplog size, rejoin the replica set and perform a complete initial sync.

Now, you wouldn’t want to do this on a huge production database but if your database isn’t too large, it’ll save you a bit of reading.

More consistent iteration times

March 10, 2011

We were doing some quick and dirty load testing the other day, using a simple shell script to load messages into a queue in batches. The code looked something like:

while something ;do
echo Sending messages $(date)
sleep 5

It seemed to be working but every few iterations, the time would skip by 6 seconds instead of 5. Obviously, the time it took to send the messages and do some other stuff was adding up. Since we’re in quick and dirty mode anyway, my first instinct was to run the send-messages asynchronously (the other stuff was printing log output and had to run in sequence), so we just added an & to the end of the send-messages line and the number of skips dropped by about a third.

This was an improvement but we were still skipping pretty often and we realized we could do even better.

Rather than using sleep to add a delay, we realized we could use it to act more like a timer. We started the sleep in the background at the top of the loop body and called wait once the body of the loop was done and ready to pause for the remaining time. It was a simple change:

while something ;do
sleep 5 &
echo Sending messages $(date)
wait $slp

This kept each loop iteration really close to the 5 second goal. We might still see some drift over time but it was good enough for our purposes.

Running the latest Bing on “not supported” devices

May 14, 2010

There’s a new version of Bing available here that supports speech input and turn-by-turn spoken directions. It even seems to have traffic avoidance. I’ve barely had a chance to play with it yet but I wanted to pass along a fix for the “Your device has been identified as not supported.” error you’ll get on any but the very latest phones.

Go to the Bing install directory, mine was “\Storage Card\Program Files\Bing”, and edit the file “Bing.config”. Find the entry “UseAppServerUpdates”. Change the value from “True” to “False”. Save the file.

That should do it. The application runs now and I don’t get the error anymore.

This was tested on an HTC Kaiser running some 6.5 ROM.