Reorder DBIter fields to reduce memory usage #5078
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siying
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Mar 20, 2019
db/db_iter.cc
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| Slice prefix_start_key_; | ||
| Direction direction_; | ||
| bool arena_mode_; |
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This parameter is only used when destructor. Maybe move it to the end of the boolean area?
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@maysamyabandeh is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.
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@maysamyabandeh merged this pull request in c84fad7. |
vagogte
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Jun 18, 2019
Summary: The patch reorders DBIter fields to put 1-byte fields together and let the compiler optimize the memory usage by using less 64-bit allocations for bools and enums. This might have a negative side effect of putting the variables that are accessed together into different cache lines and hence increasing the cache misses. Not sure what benchmark would verify that thought. I ran simple, single-threaded seekrandom benchmarks but the variance in the results is too much to be conclusive. ./db_bench --benchmarks=fillrandom --use_existing_db=0 --num=1000000 --db=/dev/shm/dbbench ./db_bench --benchmarks=seekrandom[X10] --use_existing_db=1 --db=/dev/shm/dbbench --num=1000000 --duration=60 --seek_nexts=100 Pull Request resolved: facebook#5078 Differential Revision: D14562676 Pulled By: maysamyabandeh fbshipit-source-id: 2284655d46e079b6e9a860e94be5defb6f482167
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The patch reorders DBIter fields to put 1-byte fields together and let the compiler optimize the memory usage by using less 64-bit allocations for bools and enums.
This might have a negative side effect of putting the variables that are accessed together into different cache lines and hence increasing the cache misses. Not sure what benchmark would verify that thought. I ran simple, single-threaded seekrandom benchmarks but the variance in the results is too much to be conclusive.
./db_bench --benchmarks=fillrandom --use_existing_db=0 --num=1000000 --db=/dev/shm/dbbench
./db_bench --benchmarks=seekrandom[X10] --use_existing_db=1 --db=/dev/shm/dbbench --num=1000000 --duration=60 --seek_nexts=100