Common Interview Questions and Answers: A Cautionary Tale for Developers

The author shares a collection of interview questions encountered at three companies, providing personal answers and reflections to highlight common knowledge gaps among developers.

MySQL: mysql_real_escape_string requires an active connection and respects the connection charset, unlike mysql_escape_string. Both are deprecated in favor of mysqli or PDO for better performance and security.

JavaScript memory leaks: Leaks occur when allocated memory cannot be reclaimed, often due to lingering event listeners, closures retaining variables, accidental globals, or nested references. Proper reference counting and garbage collection are essential.

Closures and scope: A closure is a function that retains access to its outer lexical scope. It is unrelated to the prototype chain, which handles inheritance, while the scope chain governs variable lookup.

Concurrency example: To limit a prize pool of one million items to three draws per user, the author suggests pre‑inserting records, using atomic increments in Memcache, or employing Redis queues and MySQL exclusive locks. Sample transaction flow:

begin
查询用户抽奖次数，加排他锁
对用户抽奖次数的更新/插入
锁行查询发放情况
获得抽奖结果（动态调整概率）
更新发放表
插入中奖记录
commit

Additional topics include IP spoofing limits, port count calculations, data link layer CRC checks, B+‑tree vs hash‑table index complexity, Apache‑PHP SAPI modes, PHP's reference‑counted garbage collector, jQuery Sizzle basics, SeaJS module mapping, Memcache vs Redis differences, MD5 reversal via dictionary attacks, protected‑to‑private method overrides causing fatal errors, detailed browser request/response steps, keep‑alive long‑connection behavior, and a brief note on Linux compression commands.

The piece concludes with design challenges such as building a relay server, comparing MyISAM and InnoDB, diagnosing PHP process deadlocks, and reflecting on the importance of continuous learning for seasoned developers.