Dbs Maintenance: Fill & Download for Free

There are multiple approaches and a few important factors to keep in mind.You need to ask the following question of your company, which I refer to as Company C:Does Company C allow for planned site maintenance windows? Essentially, is it acceptable to the business and to its customers to shutdown the site or services for a period of say 2-10 hours while Database X is migrated to Database Y? For most enterprise use-cases, this is acceptable. For non-enterprise use-cases, such as an eCommerce, B2C, or Social/Professional Networking site, this is not acceptable. I was responsible for this specific migration at Netflix, where a maintenance downtime was not allowed. I've been a spectator at LinkedIn and eBay, similar migrations took place and where such a planned downtime is not permitted.Approach if Maintenance Windows are PermittedIf you can allow for a maintenance window, then your problem is much easier to solve.You first stop all traffic to the DB -- some read traffic is fine, but no write traffic is permittedNext, take a dump of the Database X (source)It is assumed that you have written an application to either convert the source dump to the destination dump or bulk load (via bulk load APIs) the destination DB from the source dump. Whichever of these 2 approaches you implement, you will run this applicationOnce this completes, you will run a validation application : again, this is something that you would need to have written and prepared ahead of time. In this validation application, you will compare tables (usually row counts) across all tablesOnce these pass, you will re-configure all client applications to talk to the new DB.If your company has written all of the client applications, then it is preferable to have them all single-read but dual-write. In other words, they should all read from the new DB but write to both the new and old DBs for some period of time (e.g. say a month). This gives you an out if you need to switch back the old DB.The approach above, with the exception of Step 6, is what enterprise DB migrations look like. In those cases, since the DB client applications are usually 3rd party applications, the IT organization is not able to set up dual writes. Hence, switching back to the old db is much more work than detailed above and usually not something they would do anyway.Approach if Maintenance Windows are Not PermittedIn most web companies (e.g. Google. Facebook, LinkedIn, Netflix, eBay, etc...), db maintenance windows are not permitted. Maintenance windows occur outside business hours and, since these are global websites, business never ceases.There are multiple approaches, but I will detail the most straight-forward of them here :1. All of these businesses take periodic DB backups of the Source DB. These are usually stored in a SAN or network file system (e.g. NFS) or some distributed object store (e.g. AWS S3)2. In addition to the dumps, all writes that have occurred after the dump was taken need to be queued somewhere!3. Again, you need to write an application that either converts a source dump (e.g. db backup) to a destination dump or bulk loads data into the destination DB. Run this application on the DB backup. When it completes, Database Y (destination) will have all data as of Database X's (source) backup, but none of the writes afterwards!4. You then need another application to drain the queue of writes (e.g. all writes after the DB backup) and apply those changes to Database Y!5. How you implement the queue is very important. It could be via database triggers on your source DB that writes to journal tables. It could also be something like Kafka or other pub-sub system.6. If you followed the DB trigger approach, then you can migrate applications over time to read-from and write-to the new DB at your own convenience (e.g. months). Until it is completed, yet-to-be-migrated applications will continue to read-from and write-to the old DB and you will need to keep running your "queue drainer" application to keep the databases in sync. Your "queue drainer" application acts as a database replication channel!7. In terms of validating your DBs, this can be challenging as database changes are essentially always inflight (except for the original copy of the source db backup). To solve this, you need to build a validating application that constantly compares both DBs (source and destination) for discrepancies or inconsistencies. The checks need to be time invariant. I wrote one for the Netflix data migration and it worked like a charm. It helped us detect a data inconsistency as well as confirm the fix for it.

I am borderline INTJ / INFJ but I try to give you an answer:INTJs are extremely independent and private people. So you will need to accept a lot of things about them.They may not answer your message straight away. But they always will. It can take hours or in my case sometimes even days to reply. Depends on my introvert mode.We disappear. Yes this is very annoying for many people who tries to be our friends. We just stop existing and you will know nothing about us. Then will come back like nothing happened and we keep on with the conversation. If you get offended and question our behavior we may get irritated. (we are independent)They will always help you with your problems. INTJ more likely will give you solutions with a logical approach to your problem instead of giving emotional support. Emotional support is just a temporary fix. We don’t really see the point of it. We want a long term bullet proof solution.We will always answer to your questions as accurate as we can. We will seriously think about what matters to you and will try to come up with a good advice/answer.You can 100% trust us. We don’t have many friends and we don’t see the point of gossiping. Whatever you tell us it will stay with us.We don’t get involved in emotional drama. Again we don’t really see the point of having intense emotional reactions. If we start arguing with someone it will have a logical background. We will stay objective and will hit you with our well and carefully thought out reasonings. But shouting? Being dramatic? Nope.You will see our goofy side and we will hit you with our dark humor which people tend to find offensive. We have a kinda icy exterior that we show and which is often misunderstood as being an arrogant superior a*ss. But in reality we are very warm, caring and loyal people who are very emotional beings. It just runs really deep and we prefer not to show it.We will hardly ask your help. Don’t get annoyed about it. INTJ people are very self-sufficient. BUT we are very happy if you do offer help. We just may turn it down.And lastly we are very low maintenance friends. You don’t have to entertain us or have multiple meetups in a week. We don’t get mad at all.These points are true when you are our friends. Not sure if every INTJ but I certainly treat differently my significant other.But in conclusion I think INTJ friendship is a very good thing to have. But depends on you as well as what you are looking for in a friend. Gossip, party, casual chit chat is not our “speciality”.

1. Know your design patterns.If you have not read Design Patterns: Elements of Reusable Object Oriented Software then do it now.2. Java is not enough.It is the rare system that will be 100% Java.- At very least there will be a DB. Learn your DBs.Pros/Cons for the different DBs themselves and then specifically when interfacing with Java- Learn different architectures/environments, especially with regard to JRE/JVM differences. At very least Windows and Linux- Learn a healthy dose of TCP and UDP, you are not expected to be a Networking expert but if you are going to architect systems most likely you will end up communicating with external services of some type and should know the basic differences here and when you can use UDP to improve efficiency- Learn Python, while Python is NOT ONLY a scripting language, for you as a Java dev it will be just that. A system often has maintenance and deployment issue best handled by scripts and you DONT want to use Java for that.Just a few ideas, I'm sure there are lots more but in general, the more things you know aside from Java will make you a better architect even for a Java centric project.