apache/hadoop · error · IllegalArgumentException

Attempt to seek before the begin location.

Error message

Attempt to seek before the begin location.

What it means

Thrown by the Scanner's private seekTo(Location) when the target location sorts before the scanner's begin location. A Scanner is created over a [begin, end) range of the TFile, and every seek must land inside that range; seeking earlier violates the window contract and raises IllegalArgumentException. It is usually reached through public seek methods that compute a Location from a key or offset.

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/file/tfile/TFile.java:1408

          // sorry, we must seek to a different location first.
          seekTo(l);
        }

        return inBlockAdvance(key, beyond);
      }

      /**
       * Move the cursor to the new location. The entry returned by the previous
       * entry() call will be invalid.
       * 
       * @param l
       *          new cursor location. It must fall between the begin and end
       *          location of the scanner.
       * @throws IOException
       */
      private void seekTo(Location l) throws IOException {
        if (l.compareTo(beginLocation) < 0) {
          throw new IllegalArgumentException(
              "Attempt to seek before the begin location.");
        }

        if (l.compareTo(endLocation) > 0) {
          throw new IllegalArgumentException(
              "Attempt to seek after the end location.");
        }

        if (l.compareTo(endLocation) == 0) {
          parkCursorAtEnd();
          return;
        }

        if (l.getBlockIndex() != currentLocation.getBlockIndex()) {
          // going to a totally different block
          initBlock(l.getBlockIndex());
        } else {
          if (valueChecked) {

View on GitHub (pinned to 2add963021)

Solutions

1. Create the scanner over the full file range (reader.begin() to reader.end()) when you need arbitrary seeks
2. When scanning a sub-range, only seek to locations you obtained from that same scanner/reader and that are >= its begin location
3. Clamp the computed target: if it precedes begin, seek to begin instead (or skip the seek)

Example fix

// before
Scanner scanner = reader.createScanner(beginLoc, endLoc);
scanner.seekTo(someKey); // IllegalArgumentException if key maps before beginLoc

// after
Scanner full = reader.createScanner(); // whole file: begin == reader.begin()
full.seekTo(someKey);

// Give the scanner the full range when seeks are unrestricted
Scanner scanner = reader.createScanner(); // begin == reader.begin(), end == reader.end()
scanner.seekTo(key, 0, key.length);

// Or, for a sub-range scanner, verify the key falls inside before seeking

catch (IllegalArgumentException e) {
  if (e.getMessage() != null && e.getMessage().contains("before the begin location")) {
    // target precedes the window: re-create the scanner with a wider begin range
  }
}

When it happens

Trigger: Constructing a scanner over a sub-range (e.g. one block or a byte range) and then seeking to a key or record that lives before that range's start; computing a Location from offsets of a different reader/file.

Common situations: Splitting a TFile range for parallel scanning and seeking outside the assigned split; mixing up begin/end arguments when creating the scanner (order or swapped values); reusing locations from a stale reader after the file changed.

Related errors

• Attempt to seek after the end location.
• Seeking in unsorted TFile
• No key-value to read
• Cannot seek to a negative offset " + targetPos
• Attempted to seek or read past the end of the file " + targe

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/a6c6fddc950eece7. Report an issue: GitHub.