expose a hook to skip tables during iteration#2265
expose a hook to skip tables during iteration#2265benesch wants to merge 1 commit intofacebook:masterfrom
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@yiwu-arbug has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator. |
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@benesch updated the pull request - view changes - changes since last import |
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@benesch Thank you for your contribution! Can you send the first commit as a separate PR? I think it should be a separate fix. Also can you give more explanation of the segfault (stacktrace maybe)? Thanks! @siying @IslamAbdelRahman Any comment on the rest of the PR? Thanks. |
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This is a really good idea |
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@benesch updated the pull request - view changes - changes since last import |
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Thanks for the review! I've opened #2347 to track the misalignment in the arena allocator, and updated the comment on the |
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LGTM, @yiwu-arbug, can you please check the tests and land
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@yiwu-arbug has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator. |
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Can you rebase? |
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@benesch updated the pull request - view changes - changes since last import |
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cc @mikhail-antonov - this may be useful for your incremental replication. |
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@benesch has updated the pull request. |
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@benesch has updated the pull request. |
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Ok, rebased! Would also love to get this merged. Afraid that #2347 is absolutely necessary, though; otherwise, the |
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The long-standing test failure in #2347 is finally resolved, so I don't think there any remaining blockers! |
Summary: As raised in #2265, the arena allocator will return memory that is improperly aligned to store a `std::function` on macOS. Oddly, I'm unable to tickle this bug without adding a `std::function` field to `struct ReadOptions`—but my proposal in #2265 does exactly that. In any case, here's a simple reproduction. Apply this bogus patch to get a `std::function` into `struct ReadOptions` ``` --- a/include/rocksdb/options.h +++ b/include/rocksdb/options.h @@ -1035,6 +1035,8 @@ struct ReadOptions { // Default: 0 uint64_t max_skippable_internal_keys; + std::function<void()> foo; + ReadOptions(); ReadOptions(bool cksum, bool cache); }; ``` then compile `db_properties_test` *with ubsan* and run `ReadLatencyHistogramByLevel`: ``` $ make COMPILE_WITH_UBSAN=1 db_properties_test $ ./db_properties_test --gtest_filter=DBPropertiesTest.ReadLatencyHistogramByLevel ``` ubsan will complain about several misaligned accesses: ``` Note: Google Test filter = DBPropertiesTest.ReadLatencyHistogramByLevel [==========] Running 1 test from 1 test case. [----------] Global test environment set-up. [----------] 1 test from DBPropertiesTest [ RUN ] DBPropertiesTest.ReadLatencyHistogramByLevel util/coding.h:372:12: runtime error: load of misaligned address 0x00010d85516c for type 'const unsigned long', which requires 8 byte alignment 0x00010d85516c: note: pointer points here 01 00 34 57 00 00 00 00 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 24 82 0a 01 00 00 00 ^ util/coding.h:362:3: runtime error: store to misaligned address 0x7fff5733fac4 for type 'unsigned long', which requires 8 byte alignment 0x7fff5733fac4: note: pointer points here 01 00 00 00 00 00 00 00 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 80 1d 96 0d 01 00 00 00 ^ util/coding.h:372:12: runtime error: load of misaligned address 0x00010d85516c for type 'const unsigned long', which requires 8 byte alignment 0x00010d85516c: note: pointer points here 01 00 34 57 00 00 00 00 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 24 82 0a 01 00 00 00 ^ version_set.cc:854: runtime error: constructor call on misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ version_set.cc:512: runtime error: constructor call on misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ version_set.cc:505: runtime error: constructor call on misaligned address 0x00010dbfa5e8 for type 'rocksdb::ReadOptions', which requires 16 byte alignment 0x00010dbfa5e8: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ options.h:931: runtime error: constructor call on misaligned address 0x00010dbfa5e8 for type 'rocksdb::ReadOptions', which requires 16 byte alignment 0x00010dbfa5e8: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ options.h:931: runtime error: constructor call on misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment 0x00010dbfa628: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ functional:1583: runtime error: constructor call on misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment 0x00010dbfa628: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1585:9: runtime error: member access within misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment 0x00010dbfa628: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1585:9: runtime error: store to misaligned address 0x00010dbfa648 for type '__base *' (aka '__base<void ()> *'), which requires 16 byte alignment 0x00010dbfa648: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ db/version_set.cc:864:29: runtime error: upcast of misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 a0 db 70 0a 01 00 00 00 00 00 00 00 00 00 00 00 90 14 98 0d 01 00 00 00 00 00 00 00 ^ db/version_set.cc:521:12: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 a0 db 70 0a 01 00 00 00 00 00 00 00 00 00 00 00 90 14 98 0d 01 00 00 00 00 00 00 00 ^ db/version_set.cc:521:12: runtime error: load of misaligned address 0x00010dbfa5d8 for type 'rocksdb::TableCache *', which requires 16 byte alignment 0x00010dbfa5d8: note: pointer points here 00 00 00 00 90 14 98 0d 01 00 00 00 00 00 00 00 00 00 00 00 01 01 ff ff ff ff ff ff 00 00 00 00 ^ db/version_set.cc:522:9: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 a0 db 70 0a 01 00 00 00 00 00 00 00 00 00 00 00 90 14 98 0d 01 00 00 00 00 00 00 00 ^ db/version_set.cc:522:9: runtime error: reference binding to misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment 0x00010dbfa5e8: note: pointer points here 00 00 00 00 01 01 ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ db/version_set.cc:522:24: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 a0 db 70 0a 01 00 00 00 00 00 00 00 00 00 00 00 90 14 98 0d 01 00 00 00 00 00 00 00 ^ db/version_set.cc:522:38: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 a0 db 70 0a 01 00 00 00 00 00 00 00 00 00 00 00 90 14 98 0d 01 00 00 00 00 00 00 00 ^ db/version_set.cc:522:57: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 a0 db 70 0a 01 00 00 00 00 00 00 00 00 00 00 00 90 14 98 0d 01 00 00 00 00 00 00 00 ^ db/version_set.cc:522:57: runtime error: load of misaligned address 0x00010dbfa678 for type 'rocksdb::RangeDelAggregator *', which requires 16 byte alignment 0x00010dbfa678: note: pointer points here 01 00 00 00 d0 a1 bf 0d 01 00 00 00 00 00 00 00 00 00 00 00 f8 db 70 0a 01 00 00 00 00 00 00 00 ^ db/version_set.cc:523:54: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 a0 db 70 0a 01 00 00 00 00 00 00 00 00 00 00 00 90 14 98 0d 01 00 00 00 00 00 00 00 ^ db/version_set.cc:523:54: runtime error: load of misaligned address 0x00010dbfa668 for type 'rocksdb::HistogramImpl *', which requires 16 byte alignment 0x00010dbfa668: note: pointer points here 01 00 00 00 c8 88 a5 0d 01 00 00 00 00 00 00 00 01 00 00 00 d0 a1 bf 0d 01 00 00 00 00 00 00 00 ^ db/version_set.cc:524:9: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 a0 db 70 0a 01 00 00 00 00 00 00 00 00 00 00 00 90 14 98 0d 01 00 00 00 00 00 00 00 ^ db/version_set.cc:524:47: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 a0 db 70 0a 01 00 00 00 00 00 00 00 00 00 00 00 90 14 98 0d 01 00 00 00 00 00 00 00 ^ db/version_set.cc:524:62: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 a0 db 70 0a 01 00 00 00 00 00 00 00 00 00 00 00 90 14 98 0d 01 00 00 00 00 00 00 00 ^ db/table_cache.cc:228:33: runtime error: reference binding to misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment 0x00010dbfa5e8: note: pointer points here 00 00 00 00 01 01 ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ table/block_based_table_reader.cc:1554:41: runtime error: reference binding to misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment 0x00010dbfa5e8: note: pointer points here 00 00 00 00 01 01 ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ table/block_based_table_reader.cc:1396:21: runtime error: reference binding to misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment 0x00010dbfa5e8: note: pointer points here 00 00 00 00 01 01 ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ include/rocksdb/options.h:931:8: runtime error: reference binding to misaligned address 0x00010dbfa628 for type 'const std::function<void ()>', which requires 16 byte alignment 0x00010dbfa628: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1584:13: runtime error: load of misaligned address 0x00010dbfa648 for type '__base *const' (aka '__base<void ()> *const'), which requires 16 byte alignment 0x00010dbfa648: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 c8 a5 97 0d 01 00 00 00 38 36 9b 0d ^ table/block_based_table_reader.cc:1555:24: runtime error: reference binding to misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment 0x00010dbfa5e8: note: pointer points here 00 00 00 00 01 01 ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ db/table_cache.cc:244:54: runtime error: load of misaligned address 0x00010dbfa618 for type 'const bool', which requires 16 byte alignment 0x00010dbfa618: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ db/table_cache.cc:246:49: runtime error: reference binding to misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment 0x00010dbfa5e8: note: pointer points here 00 00 00 00 01 01 ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ db/version_set.cc:532:12: runtime error: member access within misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 a0 db 70 0a 01 00 00 00 00 00 00 00 00 00 00 00 90 14 98 0d 01 00 00 00 00 00 00 00 ^ db/version_set.cc:532:12: runtime error: member access within misaligned address 0x00010dbfa5e8 for type 'const rocksdb::ReadOptions', which requires 16 byte alignment 0x00010dbfa5e8: note: pointer points here 00 00 00 00 01 01 ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ db/version_set.cc:532:26: runtime error: load of misaligned address 0x00010dbfa5f8 for type 'const rocksdb::Slice *const', which requires 16 byte alignment 0x00010dbfa5f8: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ version_set.cc:493: runtime error: member call on misaligned address 0x00010dbfa5c8 for type 'rocksdb::(anonymous namespace)::LevelFileIteratorState', which requires 16 byte alignment 0x00010dbfa5c8: note: pointer points here 00 00 00 00 a0 db 70 0a 01 00 00 00 00 00 00 00 00 00 00 00 90 14 98 0d 01 00 00 00 00 00 00 00 ^ version_set.cc:493: runtime error: member call on misaligned address 0x00010dbfa5e8 for type 'rocksdb::ReadOptions', which requires 16 byte alignment 0x00010dbfa5e8: note: pointer points here 00 00 00 00 01 01 ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ options.h:931: runtime error: member call on misaligned address 0x00010dbfa5e8 for type 'rocksdb::ReadOptions', which requires 16 byte alignment 0x00010dbfa5e8: note: pointer points here 00 00 00 00 01 01 ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ options.h:931: runtime error: member call on misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment 0x00010dbfa628: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ functional:1765: runtime error: member call on misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment 0x00010dbfa628: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1766:9: runtime error: member access within misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment 0x00010dbfa628: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1766:9: runtime error: load of misaligned address 0x00010dbfa648 for type '__base *' (aka '__base<void ()> *'), which requires 16 byte alignment 0x00010dbfa648: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 c8 a5 97 0d 01 00 00 00 38 36 9b 0d ^ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1766:27: runtime error: member access within misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment 0x00010dbfa628: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1768:14: runtime error: member access within misaligned address 0x00010dbfa628 for type 'std::__1::function<void ()>', which requires 16 byte alignment 0x00010dbfa628: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:1768:14: runtime error: load of misaligned address 0x00010dbfa648 for type '__base *' (aka '__base<void ()> *'), which requires 16 byte alignment 0x00010dbfa648: note: pointer points here 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 c8 a5 97 0d 01 00 00 00 38 36 9b 0d ^ [ OK ] DBPropertiesTest.ReadLatencyHistogramByLevel (1599 ms) [----------] 1 test from DBPropertiesTest (1599 ms total) [----------] Global test environment tear-down [==========] 1 test from 1 test case ran. (1599 ms total) [ PASSED ] 1 test. ``` So it seems the root cause is that the internal implementation of `std::function` on macOS (and perhaps with libc++ generally?) requires 16-byte aligned memory, but the arena allocator only guarantees that the returned memory will be `sizeof(void*)` aligned, which is only 8-byte alignment on my machine. This patch solves the problem by adjusting the allocator to derive the necessary alignment from `alignof(std::max_align_t)`, which is properly 16 bytes on my machine. As I mentioned in #2265, none of RocksDB's tests will cause this unaligned access to actually abort the process, but, on macOS, linking CockroachDB against a version of RocksDB with the above patch and letting it run for just a few seconds will cause a SIGABRT. ``` Process 19792 stopped * thread #2, stop reason = EXC_BAD_ACCESS (code=EXC_I386_GPFLT) frame #0: 0x0000000004f5e78f cockroach`DBNewIter + 95 cockroach`DBNewIter: -> 0x4f5e78f <+95>: callq *0x28(%rax) 0x4f5e792 <+98>: jmp 0x4f5e79e ; <+110> 0x4f5e794 <+100>: movq -0x50(%rbp), %rcx 0x4f5e798 <+104>: movq %rax, %rdi (lldb) bt * thread #2, stop reason = EXC_BAD_ACCESS (code=EXC_I386_GPFLT) * frame #0: 0x0000000004f5e78f cockroach`DBNewIter + 95 ``` I'd get you a backtrace, but [Go doesn't include cgo debug information on macOS](golang/go#6942). I've also tried building against libc++ on Linux, where debug information would be available, but I can't seem to trigger the bug there. In any case, this PR both fixes the segfault in CockroachDB and fixes the warnings reported by ubsan. Closes #2347 Differential Revision: D5108596 Pulled By: yiwu-arbug fbshipit-source-id: bd5e4323b2ce915ed4fe78e123cb8996aec75a00
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@benesch has updated the pull request. |
Add a `table_filter` to `ReadOptions` that allows specifying a callback to be executed during iteration before each table in the database is scanned. The callback is passed the table's properties; the table is scanned iff the callback returns true. This can be used in conjunction with a `TablePropertiesCollector` to dramatically speed up scans by skipping tables that are known to contain irrelevant data for the scan at hand. Under ideal conditions, this feature can reduce the time of an incremental backup in CockroachDB from hours to seconds.
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@benesch has updated the pull request. |
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@yiwu-arbug is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.
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Thanks for merging this @yiwu-arbug . |
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Thanks guys! Glad to see it landed. I definitely can make use of it. |
As discussed on the mailing list ("Skipping entire SSTs while iterating"), this patch adds a
table_filtertoReadOptionsthat allows specifying a callback to be executed during iteration before each table in the database is scanned. The callback is passed the table's properties; the table is scanned iff the callback returns true.This can be used in conjunction with a
TablePropertiesCollectorto dramatically speed up scans by skipping tables that are known to contain irrelevant data for the scan at hand.We're using this downstream in CockroachDB already. With this feature, under ideal conditions, we can reduce the time of an incremental backup in from hours to seconds.
FYI, the first commit in this PR fixes a segfault that I unfortunately have not figured out how to reproduce outside of CockroachDB. I'm hoping you accept it on the grounds that it is not correct to return 8-byte aligned memory from a call to
mallocon some 64-bit platforms; one correct approach is to infer the necessary alignment fromstd::max_align_t, as done here. As noted in the first commit message, the bug is tickled by having astd::functioninstruct ReadOptions. That is, the following patch alone is enough to cause RocksDB to segfault when run from CockroachDB on Darwin./cc @danhhz