What to do if the database loads at 100% every 30 minutes? How to solve the heavy analytical query problem?
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235
Node.js
How to process parallel balance deduction operations sequentially to avoid double deduction (race condition)?
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232
Why did you choose an object for storing subscribers? How does unsubscription through filter work? What is the algorithm complexity of filter?
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199
/* * Implement an EventEmitter. * With methods emit and on. * * on(eventName: string | Symbol, callback: (payload?: any) => void): * () => void; * Takes an event name and a callback function. * The function subscribes to the event. * The result of the function should be an unsubscribe function. * * emit(eventName: string | Symbol, payload?: any): void * Takes an event name and a payload that will * be passed to each listener of eventName; the function triggers the event. * If no listener is found, it should throw an exception. * * ------------------------------------------------------ * * Example: * const myEmitter = new EventEmitter(); * * const unSubscribe = myEmitter.on('event', (payload) => { * console.log('an event occurred!!!', payload); */
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191
What are the purposes of indexes in PostgreSQL?
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185
Tell about the principles of ACID in relational databases.
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174
// [DATABASE] Design a database for users and their electronic wallets. // A user can own multiple electronic wallets in different currencies, but cannot own two wallets in the same currency. // Possible currencies: USD/EUR/RUB. The wallet should contain the current balance; // Currencies should have an additional name in Russian.
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173
What are connection pools in the context of working with databases, and what are they used for?
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173
What are FK and UNIQUE constraints in a database?
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167
What levels of transaction isolation do you know and what do they mean?
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164
Why choose FLOAT type for balance? How does it differ from DECIMAL? What changes if INTEGER is used?
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160
Tell us about your experience with monitoring and logging (Grafana, Kibana)
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153
// 2. Formulate a query to select users who do not have a EUR wallet.
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152
What is the difference between synchronous and asynchronous code?
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152
What is the difference between Map and WeakMap?
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151
What is Node.js and what does it consist of?
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150
// The user may own multiple electronic wallets in different currencies, but cannot own two wallets in the same currency. // Possible currencies: USD/EUR/RUB. The wallet must contain the current balance; // Currencies should have an additional name in Russian. // ADD Currency -> BTC/ETH/TON // ADD language ES/FR/EN User { id int PK string email string } Currency { code varchar(3) PK // USD, EUR, RUB name_ru string optional type enum('fiat', 'crypto') } CurrencyTranslations { } Wallet { user_id FK (User.id) currency_code FK (Currency.code) balance decimal }
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138
Name the promise methods (Promise.resolve, Promise.reject, and others)
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133
What is an EventEmitter and how does it work?
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128
What type of relationship will there be between the books and authors tables?
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118