{"record":{"id":"a6c6fddc950eece7","repo":"apache/hadoop","slug":"attempt-to-seek-before-the-begin-location","errorCode":null,"errorMessage":"Attempt to seek before the begin location.","messagePattern":"Attempt to seek before the begin location\\.","errorType":"exception","errorClass":"IllegalArgumentException","httpStatus":null,"severity":"error","filePath":"hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/file/tfile/TFile.java","lineNumber":1408,"sourceCode":"          // sorry, we must seek to a different location first.\n          seekTo(l);\n        }\n\n        return inBlockAdvance(key, beyond);\n      }\n\n      /**\n       * Move the cursor to the new location. The entry returned by the previous\n       * entry() call will be invalid.\n       * \n       * @param l\n       *          new cursor location. It must fall between the begin and end\n       *          location of the scanner.\n       * @throws IOException\n       */\n      private void seekTo(Location l) throws IOException {\n        if (l.compareTo(beginLocation) < 0) {\n          throw new IllegalArgumentException(\n              \"Attempt to seek before the begin location.\");\n        }\n\n        if (l.compareTo(endLocation) > 0) {\n          throw new IllegalArgumentException(\n              \"Attempt to seek after the end location.\");\n        }\n\n        if (l.compareTo(endLocation) == 0) {\n          parkCursorAtEnd();\n          return;\n        }\n\n        if (l.getBlockIndex() != currentLocation.getBlockIndex()) {\n          // going to a totally different block\n          initBlock(l.getBlockIndex());\n        } else {\n          if (valueChecked) {","sourceCodeStart":1390,"sourceCodeEnd":1426,"githubUrl":"https://github.com/apache/hadoop/blob/2add9630210752f88ceb1bb74eb65e37bf41da8e/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/file/tfile/TFile.java#L1390-L1426","documentation":"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.","triggerScenarios":"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.","commonSituations":"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.","solutions":["Create the scanner over the full file range (reader.begin() to reader.end()) when you need arbitrary seeks","When scanning a sub-range, only seek to locations you obtained from that same scanner/reader and that are >= its begin location","Clamp the computed target: if it precedes begin, seek to begin instead (or skip the seek)"],"exampleFix":"// before\nScanner scanner = reader.createScanner(beginLoc, endLoc);\nscanner.seekTo(someKey); // IllegalArgumentException if key maps before beginLoc\n\n// after\nScanner full = reader.createScanner(); // whole file: begin == reader.begin()\nfull.seekTo(someKey);","handlingStrategy":"validation","validationCode":"// Give the scanner the full range when seeks are unrestricted\nScanner scanner = reader.createScanner(); // begin == reader.begin(), end == reader.end()\nscanner.seekTo(key, 0, key.length);\n\n// Or, for a sub-range scanner, verify the key falls inside before seeking","typeGuard":null,"tryCatchPattern":"catch (IllegalArgumentException e) {\n  if (e.getMessage() != null && e.getMessage().contains(\"before the begin location\")) {\n    // target precedes the window: re-create the scanner with a wider begin range\n  }\n}","preventionTips":["Use full-range scanners for arbitrary key seeks; reserve sub-range scanners for sequential split processing","Derive seek locations only from the same reader and range that constructed the scanner","Double-check begin/end argument order when creating range scanners"],"tags":["hadoop","tfile","scanner","seek","out-of-range"],"backgroundTag":"seek-out-of-range","analyzedSha":"2add9630210752f88ceb1bb74eb65e37bf41da8e","analyzedAt":"2026-08-22T19:55:07.957Z","schemaVersion":2},"datasetVersion":"2026-08-23T01:17:44.959Z"}