Indexing Bit-Accurate Traces Using N-Grams for Efficient Byte Pattern Search
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Solution Overview
Problem
Existing time-travel traces lack the entire state of memory at every moment, making it challenging to efficiently search for specific byte patterns, as these patterns may not appear in the trace data stream even if they were read or written during execution.
Innovation Solution
Indexing arbitrary length values at arbitrary alignments in bit-accurate traces using n-grams, which are unique byte patterns associated with their locations and times of occurrence, allowing for efficient determination of pattern presence and timing during prior thread execution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bit-accurate traces are recorded based on processor data influxes during execution, then memory state can be incrementally modified as the original program modified memory state, but the traces do not contain the entire state of memory at every moment in time, making it challenging to search for byte patterns
Solution Approach 1:
The patent applies preliminary action by creating an index data structure during the trace recording phase. The index is built by extracting n-grams from memory states at various points in time and storing their locations and timestamps. This preliminary indexing enables efficient byte pattern searching during the debugging phase without requiring full memory snapshots at all times, thus maintaining the reliability of incremental memory state recording while solving the search difficulty.
Solution Approach 2:
The patent uses an index data structure as an intermediary between the trace data and the search query. The index contains n-grams extracted from memory states, serving as a mediator that allows the debugger to search for byte patterns efficiently. When a search query is received, the index is queried to find matching n-grams, which then point to the relevant trace locations, eliminating the need to scan the entire trace data stream.
2Productivity
If n-grams are extracted and indexed from memory states, then byte pattern searching becomes efficient, but the index data structure must associate n-grams with multiple trace locations and timestamps, increasing data structure complexity
Solution Approach 1:
The patent applies segmentation by dividing the memory state into smaller units called n-grams (sequences of n bytes). Instead of indexing entire memory states or large data structures, the system segments memory content into manageable n-byte chunks and indexes these segments. This segmentation reduces the complexity of individual index entries while enabling efficient pattern matching, as searches can be performed on the segmented n-grams rather than the complete memory state.
Solution Approach 2:
The patent utilizes parameter changes by allowing the n-gram size to be configurable. The index data structure can adapt to different n values based on search requirements. By changing the n parameter, the system can balance between index size and search precision. This parameter flexibility enables the system to optimize for different debugging scenarios without requiring a fixed complex data structure, thus managing complexity while maintaining search efficiency.
3Quantity of substance
If the trace records only processor data influxes and not full memory snapshots, then the trace size and processing overhead are reduced, but byte patterns that were read or written during execution may not appear in the trace data stream
Solution Approach 1:
The patent applies the extraction principle by extracting n-grams from memory states at specific points in time and storing them in the index data structure. Instead of storing complete memory snapshots, the system extracts only the relevant n-byte sequences that are likely to be searched for during debugging. This extraction process preserves byte pattern information while significantly reducing the quantity of trace data that needs to be stored and processed, as only the extracted n-grams and their locations are retained in the index.
Solution Approach 2:
The patent uses preliminary action by pre-extracting and indexing n-grams from memory states during the trace recording phase. This preliminary extraction ensures that byte pattern information is captured and organized in the index before the actual search operation. The index is built in advance by processing memory states as they occur during execution, so that when a search query is received, the necessary byte pattern information is already available in the index without requiring full memory snapshots.
Data Source
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AI summary
Indexing and searching a bit-accurate trace for arbitrary length/arbitrary alignment values in traced thread(s). Indexing includes, while replaying a plurality of trace segments, identifying a set of n-grams for each trace segment that exist in processor data influx(es) and/or store(s) to a processor cache that resulted from replay of the trace segment. An index data structure, which associates each identified n-gram with trace location(s) at or in which the n-gram was found, is then generated. The index data structure thus associates unique n- grams with prior execution time(s) at or during which the traced thread(s) read or wrote the n-gram. Searching an indexed trace includes identifying n-grams in a query and using the index data structure to determine trace location(s) where these n-grams were seen during indexing. A query response is generated after using trace replay to locate particular execution time(s) and memory location(s) at which the n-grams occurred.