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‫Day's topic is exclusive, Locke versus shared Locke, a very, very common topic out there and the

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‫database and the DBMS systems.

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‫So let's start with this episode.

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‫We're going to discuss the differences between them and we're going to talk about an example of some

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‫advantages, disadvantages of both.

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‫And we're going to talk about an example.

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‫A story about defining each of them.

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‫So exclusive, Locke and a shared Locke.

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‫So think of an exclusive law as following.

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‫I wanted to read a piece of data in my database.

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‫Think of it like a column or a row.

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‫But I want to make sure that when I read this value or when I want to update this value, nobody is

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‫connected.

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‫And nobody is attempting to read this value for security reason, for consistency reasons.

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‫You know, I want to acquire an exclusive privileges on this value, on this column, on this role,

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‫so that if anybody tried to read that value, they'll get an error.

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‫So you know what?

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‫So that's that's the idea of an exclusive look.

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‫So I will be the only one essentially as a connection.

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‫I'll be the only one who is allowed to update that so nobody can sneak in and start reading values out

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‫of that.

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‫Right.

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‫The shared look, on the other hand, is actually the opposite of that, is when I want to read a value

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‫from the database.

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‫When I read a certain value, I want to make sure that nobody changed that.

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‫So if I am reading my balance in a bank right, I want to make sure I'm doing the reporting.

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‫I'm doing a huge query.

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‫I want to acquire a shared look and says, Hey, database, please.

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‫I'm acquiring a shared look on this row.

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‫So if anybody's trying to edit that value, just make them fail.

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‫So I am I want this value to be always the same in my vision, in my transaction, in this current transaction.

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‫I want it to be unchanged.

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‫That's why I acquire a shared look and many users can acquire many connections, can acquire a different

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‫share.

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‫Look, I know this might sound a little vague, but I will explain.

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‫And in an example, hopefully.

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‫So let's give you an example.

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‫So, look, General, I want to obtain a lock on a value, so I am the only one who is allowed to edit

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‫it shared.

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‫Look, I want to acquire a shared log on or a read log on a value so it doesn't change.

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‫So another thing I won't explain before we got to do the example is when I try to obtain an exclusive

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‫lock, there must not be any shared lock acquired on that value.

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‫Does that make sense that they are linked actually together?

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‫And the opposite?

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‫If I want to obtain a shared log, there must not be any exclusive log obtained.

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‫So these two are exactly the opposite of each other.

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‫So you can have as let's say, for example, I have like seven shared log on on the balance on a certain

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‫value.

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‫That means nobody can acquire an exclusive lock on that value.

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‫So nobody can edit it as a sense, you know.

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‫So that's the idea.

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‫Read or write log.

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‫That makes sense.

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‫Let's jump to an example, guys.

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‫All right.

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‫So here I have three people, Alice, Bob and Charlie.

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‫Alice's Red Bob is blue, Charlie's green.

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‫And we're going to start this is the timeline from left to right.

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‫And then we're going to start with Alice started the transaction trying to deposit a two hundred dollars

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‫on her account.

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‫Right.

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‫So in order to do that, she needs obviously to do an album date statement.

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‫Right.

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‫To do that, you need to acquire an exclusive log.

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‫And that's what she's the only one issue that she's the only one that is connected right now.

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‫So she she'll basically acquire it, tries to acquire an exclusive log and guess what?

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‫To succeed because nobody else acquired any shared log.

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‫So they're good.

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‫And now you just like, move, move on and and acquire the exclusive look.

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‫She is guaranteeing that, hey, I'm on about Ed.

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‫That's good.

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‫That's good.

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‫Because I don't want people reading bad value.

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‫Right.

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‫Because I'm about to update this balance.

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‫So don't ever try to read my balance right now because it's going to change if you read.

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‫Did I make decisions based on that is going to be bad, right?

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‫So you're going to acquire that and then say, OK, I'm going to deposit.

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‫So the next transaction is essentially transaction going to come and then we're going to increase our

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‫balance by two hundred very, very quick and then commit the transaction and then have a transaction

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‫finished just a short period of time.

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‫And then you turn around Alice and then it starts another long running transaction.

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‫Look at that.

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‫Said it's a long transaction.

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‫Looks like it.

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‫Right.

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‫It's a job reporting job on her.

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‫But she is doing reading a lot.

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‫She's just doing reading operation.

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‫So a Reid operation is acquiring Shedlock.

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‫So what she says here is, hey, hey, guys, I am going to acquire a shared look on my balance account.

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‫So don't try to change it.

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‫Please don't try to mess with it.

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‫Don't try to update it because you can't, because I just acquired the shares so nobody can acquire

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‫an exclusive log on her account now because she just had a shared log there.

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‫OK, so, OK, she is doing her thing or reading all this tables and doing the reporting so that all

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‫transaction when Bob started the reporting job on his account.

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‫So that's a completely different thing.

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‫Right.

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‫So they acquired a shared log barbacoa to shared log on his account.

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‫So on this value, while while Alice acquired a show like a shared log on, this value makes sense.

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‫All right.

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‫So that succeeded.

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‫We have a lock for Bob.

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‫We have a shared log for Alice, and then we're continuing.

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‫So something is going to happen here.

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‫What is that green thing?

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‫What is going on, Charlie?

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‫Charlie, what are you going to do?

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‫Charlie wants to do a transfer to Bob account.

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‫Bob, it's your lucky day, dude.

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‫Bob's account attempt to obtain an exclusive slot but fails.

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‫Why?

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‫Because you want to do a transfer right from his account of a 300 dollars.

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‫I didn't write in there, but trying to do a three hundred dollars transfer from Charlie's account,

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‫from his account to Bob's account.

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‫So in order to do that, he needs to acquire an exclusive log.

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‫So anyone I want to update that, guys, I don't want it to change as the board would try to acquire

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‫an exclusive look on Bob's account.

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‫And he says, oh, fails.

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‫Why?

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‫Because Bob has already acquired a shared log.

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‫He's doing something.

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‫He's doing his thing.

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‫Bob is doing his job.

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‫He's reading it the all these tables.

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‫He's doing the thing.

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‫So he asked us to to to create this shared log so nobody changes his account.

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‫So guess what?

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‫Charlie just failed his transaction.

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‫He cannot do that.

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‫And that's actually good.

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‫We don't want people editing while other people are reading as just that.

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‫So that's a danger, especially with banking systems.

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‫So guess what?

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‫After a while, Bob completes his transaction, his job, his reading job, and he says, you know what,

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‫I'm done.

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‫So he releases that -- log so he's no longer a quiet Shatalov.

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‫Afterwards, Charlie attempts again to acquire exclusive love.

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‫And Stormy Zaid's says, OK, I'm going to since I just succeeded, let me quickly go ahead and acquired

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‫the log and then commit to three hundred bucks from Charlie's account to Bob.

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‫Right.

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‫So that's a general the difference between exclusive log and shared log.

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‫And there is another example that I mentioned is that while while there is exclusive look, nobody can

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‫read, so.

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‫You can you can think of this, that let's jump to the disadvantage advantages of all this thing as

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‫shared lock and exclusive lock and was introduced to to ensure consistency in the system, as you can

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‫see.

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‫I want to be consistent.

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‫When I read this value, I wanted this value to always be the same.

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‫That's a shared exclusive.

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‫When I want to attempt when I wanted to write something, I wanted nobody to be connected.

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‫Right.

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‫So next time they connect, they read the latest volume and exclusive look and shared log.

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‫In general, they are very useful to obtain consistency, especially with a banking first.

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‫And the second thing is with configurations.

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‫If like you have a central configuration system and it's a critical configuration system, obviously,

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‫and you're making changes to it, you don't want others reading stale configuration.

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‫You want people to you want to kick people out from the connection from the database and only let them

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‫read when you're done editing, essentially.

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‫Right.

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‫So you saw this this way.

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‫All the clients will always read the latest and greatest configuration values.

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‫So that's one of the benefits.

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‫The disadvantages of that obviously can cause.

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‫He suffers as a result.

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‫You can see like people.

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‫There are chances where your failures obviously all the time, especially in banking system, you see,

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‫if you go to Bank of America, sometimes you can see those great out.

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‫You can do any transactions at night, sometimes like a midnight, because they are doing their job

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‫reporting and they are doing all this shared log.

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‫So you can't really obtained exclusive like at that time.

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‫But there are times that you cannot do your transactions.

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‫Concurrency cannot be achieved because of these luck.

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‫But at the same time, they are very critical to ensure consistency.

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‫All right, guys, this is in a nutshell, exclusive lock versus share.

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‫Like I'm going to see you in the next one.

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‫Have a good day.