Skip to main content

From NOSQL to MySql (BDB to mysql) - Part3

We finally migrated 14 nodes this weekend. As there were millions of files to be migrated even after running 5 parallel thread on each node it took close to 3-4 hours per node. We were running 3 nodes at a time otherwise the db load was shooting up high. As we cant afford to have a downtime on weekdays, the migration has to happen on weekend nights. On Friday night it we were up till 6:00 AM and on Saturday night we were up till 4:00 AM. We wanted to do more nodes but the no of files per host was going overboard and I wanted to be conservative to start with, if the mysql servers can handle more then later we would consolidate shards or move them to this host. New mysql hosts are going to be provisioned next week so hoping to migrate more nodes this week.  Monday was a calm day after long time as we chose all nodes that were spiking to be migrated first.

Db loads in all DCs are low and even app nodes are low, Surprisingly slave dbs are getting pounded more than master db after last week's optimisation in code to move some heavily used queries to slave that can handle stale data,  a good sign as we can easily add more slaves to spread the load.


Master db load on one DC


Slave DB load on one DC


Part1
Part2
Part3
Part4
Part5

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
6 comments
Read more

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
Post a Comment
Read more

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 
Post a Comment
Read more