querylog: improve error reporting

internal/querylog/qlog_file.go

@@ -112,7 +112,7 @@ func (q *QLogFile) Seek(timestamp int64) (int64, int, error) {
 			// If we're testing the same line twice then most likely
 			// the scope is too narrow and we won't find anything
 			// anymore in any other file.
-			return 0, depth, fmt.Errorf("couldn't find timestamp %v: %w", timestamp, ErrTSNotFound)
+			return 0, depth, fmt.Errorf("looking up timestamp %d in %q: %w", timestamp, q.file.Name(), ErrTSNotFound)
 		} else if lineIdx == fileInfo.Size() {
 			return 0, depth, ErrTSTooLate
 		}
@@ -122,9 +122,8 @@ func (q *QLogFile) Seek(timestamp int64) (int64, int, error) {
 
 		// Get the timestamp from the query log record
 		ts := readQLogTimestamp(line)
-
 		if ts == 0 {
-			return 0, depth, fmt.Errorf("couldn't get timestamp: %w", ErrTSNotFound)
+			return 0, depth, fmt.Errorf("looking up timestamp %d in %q: record %q has empty timestamp", timestamp, q.file.Name(), line)
 		}
 
 		if ts == timestamp {
@@ -146,7 +145,7 @@ func (q *QLogFile) Seek(timestamp int64) (int64, int, error) {
 
 		depth++
 		if depth >= 100 {
-			return 0, depth, fmt.Errorf("seek depth is too high, aborting. File %s, timestamp %v: %w", q.file.Name(), timestamp, ErrTSNotFound)
+			return 0, depth, fmt.Errorf("looking up timestamp %d in %q: depth %d too high: %w", timestamp, q.file.Name(), depth, ErrTSNotFound)
 		}
 	}