Optimize BsonArray Index encoding #1673
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JAVA-5836
JAVA-5836
vbabanin changed the title 
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| As @ShaneHarvey noted in the previous PR (#1664 (comment)), Python caches 1000 consecutive array indexes. To align with that behavior across drivers, I’ve adjusted the cache size to 1000 in the Java driver. |
vbabanin commented Apr 3, 2025
| private static final int ARRAY_INDEXES_CACHE_SIZE = 256; | ||
| private static final String[] ARRAY_INDEXES_CACHE = new String[ARRAY_INDEXES_CACHE_SIZE]; | ||
| private static final int ARRAY_INDEXES_CACHE_SIZE = 1000; | ||
| private static final byte[] ARRAY_INDEXES_BUFFER; |
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In prior benchmarks, the reference-chasing layout (i.e., byte[][]) showed ~25% lower throughput compared to a flat byte[] layout, primarily due to fragmented sequential locality and indirect memory access.
rozza approved these changes Apr 3, 2025
| fail(); | ||
| } catch (BsonMaximumSizeExceededException e) { | ||
| assertEquals("Document size of 1037 is larger than maximum of 1024.", e.getMessage()); | ||
| assertEquals("Document size of 12917 is larger than maximum of 12904.", e.getMessage()); |
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Did this get missed last time? Yes it did - thanks for fixing.
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Instead of caching precomputed
Stringvalues, we now cache their corresponding byte[] representations. This avoids repeated ASCII string decoding.The single contiguous buffer approach provides better cache locality in loops, reduced memory overhead and better performance.
The array index caching implementation consumes approximately
12 KB of memory in total:Array object headers: ~48 bytesBsonArrayCodecBenchmark results:
JAVA-5836