Skip to main content

Biggest relief from NOSQL to SQL migration

This year my biggest accomplishment was to move our old NOSQL system from BDB/Cassandra to Mysql and so far its holding billions of rows and working fine.  Though this move has given me and my buddy peace and good sleep and I can now focus on other fires. But the biggest relief comes from being able to delegate some tasks to junior team and also being able to quickly script adhoc requirements quickly.

For e.g. today I got an adhoc requirement to find list of customers with > 1000 versions of a single file.  Had it been BDB I would have to write a program and then run it on each app node to find the answer and it would have taken days to get this info.  But with mysql all I had to do was to write a script that will execute a federated query and get me the output so all I need to do is run something like

nohup python sweep_all_shards.py "select pid, max(cnt) from (select customerid,file_id,count(version_id) cnt from \${SCHEMA_NAME}.version_\${TBL_SUFFIX} group by customer_id,file_id having count(version_id) >1000)a group by customerid" &


and within 6 hours the script had sweepeed all the shards and got me the result. So I had to just do some grep/awk/sed to get the answer.

Few weeks back I got some adhoc requirement to find max size of file uploaded by each customer and same I got it in less than one day whereas earlier I would have spent days getting this info.


Also one more advantage I see is that I have created a read only user on each mysql slave and  given access to production support people and as everyone knows relational database very few requirements come to me so I get more free time to work on more interesting things.

Also last night mysql server crashed twice while creating index on a 85M record table and boy the DBAs knew how to recover it whereas when it was BDB it was an Achilles hill to recover data out of it and this time Ops team did it without involving everyone and they were all confident and relaxed and BDB/Cassandra was always panic mode.

Comments

Post a Comment

Popular posts from this blog

Killing a particular Tomcat thread

Update: This JSP does not work on a thread that is inside some native code.  On many occasions I had a thread stuck in JNI code and it wont work. Also in some cases thread.stop can cause jvm to hang. According to javadocs " This method is inherently unsafe. Stopping a thread with Thread.stop causes it to unlock all of the monitors that it has locked". I have used it only in some rare occasions where I wanted to avoid a system shutdown and in some cases we ended up doing system shutdown as jvm was hung so I had a 70-80% success with it.   -------------------------------------------------------------------------------------------------------------------------- We had an interesting requirement. A tomcat thread that was spawned from an ExecutorService ThreadPool had gone Rogue and was causing lots of disk churning issues. We cant bring down the production server as that would involve downtime. Killing this thread was harmless but how to kill it, t

Adding Jitter to cache layer

Thundering herd is an issue common to webapp that rely on heavy caching where if lots of items expire at the same time due to a server restart or temporal event, then suddenly lots of calls will go to database at same time. This can even bring down the database in extreme cases. I wont go into much detail but the app need to do two things solve this issue. 1) Add consistent hashing to cache layer : This way when a memcache server is added/removed from the pool, entire cache is not invalidated.  We use memcahe from both python and Java layer and I still have to find a consistent caching solution that is portable across both languages. hash_ring and spymemcached both use different points for server so need to read/test more. 2) Add a jitter to cache or randomise the expiry time: We expire long term cache  records every 8 hours after that key was added and short term cache expiry is 2 hours. As our customers usually comes to work in morning and access the cloud file server it can happe

Preparing for an interview after being employed 11 years at a startup

I would say I didn't prepared a hell lot but  I did 2 hours in night every day and every weekend around 8 hours for 2-3 months. I did 20-30 leetcode medium problems from this list https://leetcode.com/explore/interview/card/top-interview-questions-medium/.  I watched the first 12 videos of Lecture Videos | Introduction to Algorithms | Electrical Engineering and Computer Science | MIT OpenCourseWare I did this course https://www.educative.io/courses/grokking-the-system-design-interview I researched on topics from https://www.educative.io/courses/java-multithreading-for-senior-engineering-interviews and leetcode had around 10 multithreading questions so I did those I watched some 10-20 videos from this channel https://www.youtube.com/channel/UCn1XnDWhsLS5URXTi5wtFTA