Optimize database queries, diff algorithm, and filesystem operations

[Copilot]

Identified and fixed multiple performance bottlenecks: N+1 queries, inefficient algorithms, and repeated filesystem searches.

Database Query Optimization

GetBackupStats - Eliminated N+1 pattern by combining queries and moving duration calculation to SQL:

// Before: 2 queries + loop with time parsing
rows := db.Query("SELECT started_time, completed_time FROM backups...")
for rows.Next() {
    startTime, _ := common.ParseTime(startStr)
    endTime, _ := common.ParseTime(endStr)
    duration := endTime.Sub(startTime).Minutes()
}

// After: Single query with SQL-based calculation
db.QueryRow(`
    SELECT COUNT(*), SUM(size),
    AVG(CAST((julianday(completed_time) - julianday(started_time)) * 86400 AS REAL))
    FROM backups...
`)

ListByUserID - Replaced correlated subquery with window function:

// Before: Correlated subquery executed per connection
LEFT JOIN backups b ON c.id = b.connection_id
    AND b.completed_time = (SELECT MAX(completed_time) FROM backups WHERE connection_id = c.id)

// After: Window function with single scan
LEFT JOIN (
    SELECT connection_id, completed_time,
    ROW_NUMBER() OVER (PARTITION BY connection_id ORDER BY completed_time DESC) as rn
    FROM backups
) b ON c.id = b.connection_id AND b.rn = 1

Algorithm Optimization

generateDiff - Reduced time complexity from O(n*m) to O(n+m) using hash map for line lookups instead of nested loops.

readBackupFile - Added 10MB size limit and pre-allocated buffer to prevent OOM on large files.

Caching

FindBinaryPath - Added thread-safe cache for binary path lookups to eliminate repeated glob operations and stat calls. Only caches successful lookups to allow for binaries installed later.

executeCronBackup - Uses cron.Entry.Next instead of reparsing schedule string on every execution.

Original prompt

Identify and suggest improvements to slow or inefficient code

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Project	Deployment	Preview	Comments	Updated (UTC)
velld	Ready	Preview	Comment	Oct 29, 2025 2:52am