How to Efficiently List Files in a Directory with Billions of Entries in Go?

Recursive Directory Listing with Efficiency Considerations

Problem:

Listing files in a directory with an extremely large number of entries (in the billions) using traditional Go functions like ioutil.ReadDir or filepath.Glob becomes inefficient. These functions return sorted slices, which can lead to memory exhaustion.

Solution:

Instead of relying on slices, leverage the Readdir or Readdirnames methods with a non-zero n argument to read directory entries in batches. This allows you to process a stream of os.FileInfo objects (or strings) over a channel.

Implementation:

package main

import (
    "fmt"
    "io/ioutil"
    "os"
    "path/filepath"
)

func main() {
    // Specify the directory to list.
    dir := "path/to/directory"

    // Define a channel to receive file entries.
    fileEntries := make(chan os.FileInfo)

    // Start goroutines to read directory entries in batches.
    for {
        entries, err := ioutil.ReadDir(dir)
        if err != nil {
            fmt.Println(err)
            continue
        }
        if len(entries) == 0 {
            break
        }

        // Send each file entry to the channel.
        for _, entry := range entries {
            fileEntries <- entry
        }
    }

    // Process the file entries.
    for entry := range fileEntries {
        fmt.Println(entry.Name())
    }
}

Advantages:

• Avoids memory exhaustion by streaming entries instead of returning a large sorted slice.
• Provides more control over the processing of directory entries.
• Can be tailored to perform additional tasks after reading each batch.

Note:

• This approach does not provide any guarantees on the order of the directory entries.
• You may need to consider limiting the number of concurrent goroutines to prevent overwhelming your system's resources.

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