How to Efficiently Read the Last N Lines of a File in PHP?

Optimized File Tail Reading in PHP

Objective: Obtain the last N lines from a file in an efficient manner.

Solution Approaches:

1. Naive Method:

• Utilizes the file() function to load the entire file into an array.
• Retrieves the desired number of lines from the end using array slicing.

2. External Script Reliance:

• Invokes the tail command on the system.
• Only viable if tail is available.

3. Single-Byte Search:

• Iterates through the file backwards, searching for new line characters.

4. Multi-Byte Buffer:

• Utilizes a fixed-size buffer to optimize large file reading.

5. Dynamic Buffer:

• Extends the buffer size based on the number of lines requested.

Performance Analysis:

Comparative tests were conducted on files ranging from 10 KB to 10 MB.

100 KB File:

• Dynamic buffer solution (Solution #5) exhibited the best performance for all line counts.
• Naive solution (Solution #1) was unsuitable due to potential memory exhaustion.

10 MB File:

• Solution #5 remained the most efficient choice.
• Solution #1 proved impractical due to excessive memory usage.

10 KB File:

• Naive solution (Solution #1) performed exceptionally well due to its low memory footprint.
• Solution #4 and #5 also delivered good results.

Conclusion:

For general use cases and optimal performance, Solution #5 (Dynamic Buffer) is highly recommended.

Caveats:

Solution #1 should be avoided for files larger than 10 KB to prevent memory issues.

Solutions #2 and #3 are suboptimal as #2 relies on an external command and #3 suffers from slow performance with higher line counts.

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