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InnoDB undo records scanning O(log n) complexity #17
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midenok
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Nov 19, 2021
Read of size 8 at 0x7fecf2e75fc8 by thread T2 (mutexes: write M1318): #0 tpool::thread_pool_generic::submit_task(tpool::task*) /tpool/tpool_generic.cc:823:9 (mariadbd+0x25fd2d2) #1 (anonymous namespace)::aio_uring::thread_routine((anonymous namespace)::aio_uring*) /tpool/aio_liburing.cc:173:20 (mariadbd+0x260b21b) #2 void std::__invoke_impl<void, void (*)((anonymous namespace)::aio_uring*), (anonymous namespace)::aio_uring*>(std::__invoke_other, void (*&&)((anonymous namespace)::aio_uring*), (anonymous namespace)::aio_uring*&&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/invoke.h:61:14 (mariadbd+0x260c62a) #3 std::__invoke_result<void (*)((anonymous namespace)::aio_uring*), (anonymous namespace)::aio_uring*>::type std::__invoke<void (*)((anonymous namespace)::aio_uring*), (anonymous namespace)::aio_uring*>(void (*&&)((anonymous namespace)::aio_uring*), (anonymous namespace)::aio_uring*&&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/invoke.h:96:14 (mariadbd+0x260c4ba) #4 void std::thread::_Invoker<std::tuple<void (*)((anonymous namespace)::aio_uring*), (anonymous namespace)::aio_uring*> >::_M_invoke<0ul, 1ul>(std::_Index_tuple<0ul, 1ul>) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/std_thread.h:253:13 (mariadbd+0x260c442) #5 std::thread::_Invoker<std::tuple<void (*)((anonymous namespace)::aio_uring*), (anonymous namespace)::aio_uring*> >::operator()() /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/std_thread.h:260:11 (mariadbd+0x260c3c5) #6 std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)((anonymous namespace)::aio_uring*), (anonymous namespace)::aio_uring*> > >::_M_run() /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/std_thread.h:211:13 (mariadbd+0x260c189) #7 <null> <null> (libstdc++.so.6+0xd230f) Previous write of size 8 at 0x7fecf2e75fc8 by main thread: #0 tpool::task::task(void (*)(void*), void*, tpool::task_group*) /tpool/task.cc:40:46 (mariadbd+0x260a138) #1 tpool::aiocb::aiocb() /tpool/tpool.h:147:13 (mariadbd+0x2355943) #2 void std::_Construct<tpool::aiocb>(tpool::aiocb*) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/stl_construct.h:109:38 (mariadbd+0x2355845) #3 tpool::aiocb* std::__uninitialized_default_n_1<false>::__uninit_default_n<tpool::aiocb*, unsigned long>(tpool::aiocb*, unsigned long) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/stl_uninitialized.h:579:3 (mariadbd+0x235576c) #4 tpool::aiocb* std::__uninitialized_default_n<tpool::aiocb*, unsigned long>(tpool::aiocb*, unsigned long) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/stl_uninitialized.h:638:14 (mariadbd+0x23556e9) #5 tpool::aiocb* std::__uninitialized_default_n_a<tpool::aiocb*, unsigned long, tpool::aiocb>(tpool::aiocb*, unsigned long, std::allocator<tpool::aiocb>&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/stl_uninitialized.h:704:14 (mariadbd+0x2355641) #6 std::vector<tpool::aiocb, std::allocator<tpool::aiocb> >::_M_default_initialize(unsigned long) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/stl_vector.h:1606:4 (mariadbd+0x2354f3d) #7 std::vector<tpool::aiocb, std::allocator<tpool::aiocb> >::vector(unsigned long, std::allocator<tpool::aiocb> const&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/stl_vector.h:512:9 (mariadbd+0x2354a19) #8 tpool::cache<tpool::aiocb>::cache(unsigned long, tpool::cache_notification_mode) /tpool/tpool_structs.h:73:20 (mariadbd+0x2354784) #9 io_slots::io_slots(int, int) /storage/innobase/os/os0file.cc:93:3 (mariadbd+0x235343b) #10 os_aio_init() /storage/innobase/os/os0file.cc:3780:22 (mariadbd+0x234ebce) #11 srv_start(bool) /storage/innobase/srv/srv0start.cc:1190:6 (mariadbd+0x256720c) #12 innodb_init(void*) /storage/innobase/handler/ha_innodb.cc:4188:8 (mariadbd+0x1ed3bda) #13 ha_initialize_handlerton(st_plugin_int*) /sql/handler.cc:659:31 (mariadbd+0xf7be06) #14 plugin_initialize(st_mem_root*, st_plugin_int*, int*, char**, bool) /sql/sql_plugin.cc:1463:9 (mariadbd+0x160fa1b) #15 plugin_init(int*, char**, int) /sql/sql_plugin.cc:1756:15 (mariadbd+0x160f07f) #16 init_server_components() /sql/mysqld.cc:5043:7 (mariadbd+0xd70fb2) #17 mysqld_main(int, char**) /sql/mysqld.cc:5655:7 (mariadbd+0xd6a9d7) #18 main /sql/main.cc:34:10 (mariadbd+0xd65d18) I think the report is incorrect: it's not possible to have such a race condition. I've checked it by reading the code and putting assertions. Namely, no aio I/O is possible before the end of os_aio_init(). Most probably it's some bug in TSAN. But the patch fixes around 5 related reports and this is a step toward TSAN usefullness. Currently it reports too much noise. std::unique_ptr is a step toward https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#r11-avoid-calling-new-and-delete-explicitly There is no std::make_unique() in C++11, however.
midenok
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Nov 19, 2021
WARNING: ThreadSanitizer: data race (pid=1506937) Write of size 8 at 0x0000067ab740 by thread T6: #0 buf_page_get_low(page_id_t, unsigned long, unsigned long, buf_block_t*, unsigned long, mtr_t*, dberr_t*, bool) /storage/innobase/buf/buf0buf.cc:2946:8 (mariadbd+0x2014c7f) #1 buf_page_get_gen(page_id_t, unsigned long, unsigned long, buf_block_t*, unsigned long, mtr_t*, dberr_t*, bool) /storage/innobase/buf/buf0buf.cc:3047:10 (mariadbd+0x2016216) #2 btr_cur_search_to_nth_level_func(dict_index_t*, unsigned long, dtuple_t const*, page_cur_mode_t, unsigned long, btr_cur_t*, ssux_lock_impl<true>*, mtr_t*, unsigned long) /storage/innobase/btr/btr0cur.cc:1613:10 (mariadbd+0x1fb5bff) #3 btr_pcur_open_low(dict_index_t*, unsigned long, dtuple_t const*, page_cur_mode_t, unsigned long, btr_pcur_t*, unsigned long, mtr_t*) /storage/innobase/include/btr0pcur.ic:439:8 (mariadbd+0x24ddead) #4 row_search_on_row_ref(btr_pcur_t*, unsigned long, dict_table_t const*, dtuple_t const*, mtr_t*) /storage/innobase/row/row0row.cc:1215:7 (mariadbd+0x24dd537) #5 row_purge_reposition_pcur(unsigned long, purge_node_t*, mtr_t*) /storage/innobase/row/row0purge.cc:81:23 (mariadbd+0x24c5369) #6 row_purge_reset_trx_id(purge_node_t*, mtr_t*) /storage/innobase/row/row0purge.cc:748:6 (mariadbd+0x24c90c7) #7 row_purge_record_func(purge_node_t*, unsigned char*, que_thr_t const*, bool) /storage/innobase/row/row0purge.cc:1174:4 (mariadbd+0x24c8262) #8 row_purge(purge_node_t*, unsigned char*, que_thr_t*) /storage/innobase/row/row0purge.cc:1218:18 (mariadbd+0x24c5af3) #9 row_purge_step(que_thr_t*) /storage/innobase/row/row0purge.cc:1267:3 (mariadbd+0x24c5996) #10 que_thr_step(que_thr_t*) /storage/innobase/que/que0que.cc:653:9 (mariadbd+0x23d5298) #11 que_run_threads_low(que_thr_t*) /storage/innobase/que/que0que.cc:709:25 (mariadbd+0x23d3f29) #12 que_run_threads(que_thr_t*) /storage/innobase/que/que0que.cc:729:2 (mariadbd+0x23d3bdf) #13 srv_task_execute() /storage/innobase/srv/srv0srv.cc:1692:3 (mariadbd+0x2562841) #14 purge_worker_callback(void*) /storage/innobase/srv/srv0srv.cc:1864:10 (mariadbd+0x255f361) #15 tpool::task_group::execute(tpool::task*) /tpool/task_group.cc:55:9 (mariadbd+0x260a5ca) #16 tpool::task::execute() /tpool/task.cc:47:16 (mariadbd+0x260adf6) #17 tpool::thread_pool_generic::worker_main(tpool::worker_data*) /tpool/tpool_generic.cc:550:11 (mariadbd+0x25fc590) #18 void std::__invoke_impl<void, void (tpool::thread_pool_generic::*)(tpool::worker_data*), tpool::thread_pool_generic*, tpool::worker_data*>(std::__invoke_memfun_deref, void (tpool::thread_pool_generic::*&&)(tpool::worker_data*), tpool::thread_pool_generic*&&, tpool::worker_data*&&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/invoke.h:74:14 (mariadbd+0x26061b5) #19 std::__invoke_result<void (tpool::thread_pool_generic::*)(tpool::worker_data*), tpool::thread_pool_generic*, tpool::worker_data*>::type std::__invoke<void (tpool::thread_pool_generic::*)(tpool::worker_data*), tpool::thread_pool_generic*, tpool::worker_data*>(void (tpool::thread_pool_generic::*&&)(tpool::worker_data*), tpool::thread_pool_generic*&&, tpool::worker_data*&&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/invoke.h:96:14 (mariadbd+0x2605f57) #20 void std::thread::_Invoker<std::tuple<void (tpool::thread_pool_generic::*)(tpool::worker_data*), tpool::thread_pool_generic*, tpool::worker_data*> >::_M_invoke<0ul, 1ul, 2ul>(std::_Index_tuple<0ul, 1ul, 2ul>) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/std_thread.h:253:13 (mariadbd+0x2605ecb) #21 std::thread::_Invoker<std::tuple<void (tpool::thread_pool_generic::*)(tpool::worker_data*), tpool::thread_pool_generic*, tpool::worker_data*> >::operator()() /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/std_thread.h:260:11 (mariadbd+0x2605e35) #22 std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (tpool::thread_pool_generic::*)(tpool::worker_data*), tpool::thread_pool_generic*, tpool::worker_data*> > >::_M_run() /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/std_thread.h:211:13 (mariadbd+0x2605ac9) #23 <null> <null> (libstdc++.so.6+0xd230f) Previous write of size 8 at 0x0000067ab740 by thread T8: #0 buf_page_get_low(page_id_t, unsigned long, unsigned long, buf_block_t*, unsigned long, mtr_t*, dberr_t*, bool) /storage/innobase/buf/buf0buf.cc:2946:8 (mariadbd+0x2014c7f) #1 buf_page_get_gen(page_id_t, unsigned long, unsigned long, buf_block_t*, unsigned long, mtr_t*, dberr_t*, bool) /storage/innobase/buf/buf0buf.cc:3047:10 (mariadbd+0x2016216) #2 btr_cur_search_to_nth_level_func(dict_index_t*, unsigned long, dtuple_t const*, page_cur_mode_t, unsigned long, btr_cur_t*, ssux_lock_impl<true>*, mtr_t*, unsigned long) /storage/innobase/btr/btr0cur.cc:1613:10 (mariadbd+0x1fb5bff) #3 btr_pcur_open_low(dict_index_t*, unsigned long, dtuple_t const*, page_cur_mode_t, unsigned long, btr_pcur_t*, unsigned long, mtr_t*) /storage/innobase/include/btr0pcur.ic:439:8 (mariadbd+0x24ddead) #4 row_search_on_row_ref(btr_pcur_t*, unsigned long, dict_table_t const*, dtuple_t const*, mtr_t*) /storage/innobase/row/row0row.cc:1215:7 (mariadbd+0x24dd537) #5 row_purge_reposition_pcur(unsigned long, purge_node_t*, mtr_t*) /storage/innobase/row/row0purge.cc:81:23 (mariadbd+0x24c5369) #6 row_purge_reset_trx_id(purge_node_t*, mtr_t*) /storage/innobase/row/row0purge.cc:748:6 (mariadbd+0x24c90c7) #7 row_purge_record_func(purge_node_t*, unsigned char*, que_thr_t const*, bool) /storage/innobase/row/row0purge.cc:1174:4 (mariadbd+0x24c8262) #8 row_purge(purge_node_t*, unsigned char*, que_thr_t*) /storage/innobase/row/row0purge.cc:1218:18 (mariadbd+0x24c5af3) #9 row_purge_step(que_thr_t*) /storage/innobase/row/row0purge.cc:1267:3 (mariadbd+0x24c5996) #10 que_thr_step(que_thr_t*) /storage/innobase/que/que0que.cc:653:9 (mariadbd+0x23d5298) #11 que_run_threads_low(que_thr_t*) /storage/innobase/que/que0que.cc:709:25 (mariadbd+0x23d3f29) #12 que_run_threads(que_thr_t*) /storage/innobase/que/que0que.cc:729:2 (mariadbd+0x23d3bdf) #13 trx_purge(unsigned long, bool) /storage/innobase/trx/trx0purge.cc:1271:2 (mariadbd+0x25841b4) #14 srv_do_purge(unsigned long*) /storage/innobase/srv/srv0srv.cc:1784:20 (mariadbd+0x2563224) #15 purge_coordinator_callback_low() /storage/innobase/srv/srv0srv.cc:1881:35 (mariadbd+0x2562b3b) #16 purge_coordinator_callback(void*) /storage/innobase/srv/srv0srv.cc:1910:3 (mariadbd+0x255f4ab) #17 tpool::task_group::execute(tpool::task*) /tpool/task_group.cc:55:9 (mariadbd+0x260a5ca) #18 tpool::task::execute() /tpool/task.cc:47:16 (mariadbd+0x260adf6) #19 tpool::thread_pool_generic::worker_main(tpool::worker_data*) /tpool/tpool_generic.cc:550:11 (mariadbd+0x25fc590) #20 void std::__invoke_impl<void, void (tpool::thread_pool_generic::*)(tpool::worker_data*), tpool::thread_pool_generic*, tpool::worker_data*>(std::__invoke_memfun_deref, void (tpool::thread_pool_generic::*&&)(tpool::worker_data*), tpool::thread_pool_generic*&&, tpool::worker_data*&&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/invoke.h:74:14 (mariadbd+0x26061b5) #21 std::__invoke_result<void (tpool::thread_pool_generic::*)(tpool::worker_data*), tpool::thread_pool_generic*, tpool::worker_data*>::type std::__invoke<void (tpool::thread_pool_generic::*)(tpool::worker_data*), tpool::thread_pool_generic*, tpool::worker_data*>(void (tpool::thread_pool_generic::*&&)(tpool::worker_data*), tpool::thread_pool_generic*&&, tpool::worker_data*&&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/invoke.h:96:14 (mariadbd+0x2605f57) #22 void std::thread::_Invoker<std::tuple<void (tpool::thread_pool_generic::*)(tpool::worker_data*), tpool::thread_pool_generic*, tpool::worker_data*> >::_M_invoke<0ul, 1ul, 2ul>(std::_Index_tuple<0ul, 1ul, 2ul>) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/std_thread.h:253:13 (mariadbd+0x2605ecb) #23 std::thread::_Invoker<std::tuple<void (tpool::thread_pool_generic::*)(tpool::worker_data*), tpool::thread_pool_generic*, tpool::worker_data*> >::operator()() /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/std_thread.h:260:11 (mariadbd+0x2605e35) #24 std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (tpool::thread_pool_generic::*)(tpool::worker_data*), tpool::thread_pool_generic*, tpool::worker_data*> > >::_M_run() /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/std_thread.h:211:13 (mariadbd+0x2605ac9) #25 <null> <null> (libstdc++.so.6+0xd230f) Location is global 'buf_dbg_counter' of size 8 at 0x0000067ab740 (mariadbd+0x67ab740) The obvious fix is to make counter atomic.
midenok
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Nov 19, 2021
WARNING: ThreadSanitizer: data race (pid=1510842) Write of size 8 at 0x0000067b1e98 by main thread: #0 os_file_pwrite(IORequest const&, int, unsigned char const*, unsigned long, unsigned long, dberr_t*) /storage/innobase/os/os0file.cc:2928:2 (mariadbd+0x234c5ac) #1 os_file_write_func(IORequest const&, char const*, int, void const*, unsigned long, unsigned long) /storage/innobase/os/os0file.cc:2963:20 (mariadbd+0x234c019) #2 file_os_io::write(char const*, unsigned long, st_::span<unsigned char const>) /storage/innobase/log/log0log.cc:320:10 (mariadbd+0x22eaa50) #3 log_file_t::write(unsigned long, st_::span<unsigned char const>) /storage/innobase/log/log0log.cc:434:18 (mariadbd+0x22eb1d8) #4 log_t::file::write(unsigned long, st_::span<unsigned char>) /storage/innobase/log/log0log.cc:496:29 (mariadbd+0x22ebb55) #5 log_write_buf(unsigned char*, unsigned long, unsigned long, unsigned long, unsigned long) /storage/innobase/log/log0log.cc:614:14 (mariadbd+0x22f1b51) #6 log_write(bool) /storage/innobase/log/log0log.cc:755:2 (mariadbd+0x22ed2ec) #7 log_write_up_to(unsigned long, bool, bool, completion_callback const*) /storage/innobase/log/log0log.cc:817:5 (mariadbd+0x22eca44) #8 log_checkpoint_low(unsigned long, unsigned long) /storage/innobase/buf/buf0flu.cc:1734:5 (mariadbd+0x20d37c1) #9 log_checkpoint() /storage/innobase/buf/buf0flu.cc:1787:10 (mariadbd+0x20cd155) #10 buf_flush_wait_flushed(unsigned long) /storage/innobase/buf/buf0flu.cc:1867:5 (mariadbd+0x20ccf8f) #11 log_make_checkpoint() /storage/innobase/buf/buf0flu.cc:1793:3 (mariadbd+0x20cc4c9) #12 buf_dblwr_t::create() /storage/innobase/buf/buf0dblwr.cc:216:3 (mariadbd+0x209076a) #13 srv_start(bool) /storage/innobase/srv/srv0start.cc:1685:20 (mariadbd+0x256b4aa) #14 innodb_init(void*) /storage/innobase/handler/ha_innodb.cc:4188:8 (mariadbd+0x1ed40da) #15 ha_initialize_handlerton(st_plugin_int*) /sql/handler.cc:659:31 (mariadbd+0xf7c2b6) #16 plugin_initialize(st_mem_root*, st_plugin_int*, int*, char**, bool) /sql/sql_plugin.cc:1463:9 (mariadbd+0x160fedb) #17 plugin_init(int*, char**, int) /sql/sql_plugin.cc:1756:15 (mariadbd+0x160f53f) #18 init_server_components() /sql/mysqld.cc:5043:7 (mariadbd+0xd71462) #19 mysqld_main(int, char**) /sql/mysqld.cc:5655:7 (mariadbd+0xd6ae87) #20 main /sql/main.cc:34:10 (mariadbd+0xd661c8) Previous write of size 8 at 0x0000067b1e98 by thread T3: #0 os_file_pwrite(IORequest const&, int, unsigned char const*, unsigned long, unsigned long, dberr_t*) /storage/innobase/os/os0file.cc:2928:2 (mariadbd+0x234c5ac) #1 os_file_write_func(IORequest const&, char const*, int, void const*, unsigned long, unsigned long) /storage/innobase/os/os0file.cc:2963:20 (mariadbd+0x234c019) #2 file_os_io::write(char const*, unsigned long, st_::span<unsigned char const>) /storage/innobase/log/log0log.cc:320:10 (mariadbd+0x22eaa50) #3 log_file_t::write(unsigned long, st_::span<unsigned char const>) /storage/innobase/log/log0log.cc:434:18 (mariadbd+0x22eb1d8) #4 log_t::file::write(unsigned long, st_::span<unsigned char>) /storage/innobase/log/log0log.cc:496:29 (mariadbd+0x22ebb55) #5 log_write_checkpoint_info(unsigned long) /storage/innobase/log/log0log.cc:911:14 (mariadbd+0x22edd4e) #6 log_checkpoint_low(unsigned long, unsigned long) /storage/innobase/buf/buf0flu.cc:1755:3 (mariadbd+0x20d3a3d) #7 buf_flush_sync_for_checkpoint(unsigned long) /storage/innobase/buf/buf0flu.cc:1947:7 (mariadbd+0x20d4163) #8 buf_flush_page_cleaner() /storage/innobase/buf/buf0flu.cc:2186:9 (mariadbd+0x20cdab1) #9 void std::__invoke_impl<void, void (*)()>(std::__invoke_other, void (*&&)()) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/invoke.h:61:14 (mariadbd+0x20c3aaa) #10 std::__invoke_result<void (*)()>::type std::__invoke<void (*)()>(void (*&&)()) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/invoke.h:96:14 (mariadbd+0x20c39bd) #11 void std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul>(std::_Index_tuple<0ul>) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/std_thread.h:253:13 (mariadbd+0x20c3965) #12 std::thread::_Invoker<std::tuple<void (*)()> >::operator()() /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/std_thread.h:260:11 (mariadbd+0x20c3905) #13 std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run() /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/std_thread.h:211:13 (mariadbd+0x20c37f9) #14 <null> <null> (libstdc++.so.6+0xd230f) Location is global 'os_n_file_writes' of size 8 at 0x0000067b1e98 (mariadbd+0x67b1e98) Make variable atomic.
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Implementation: undo index and binary search
DB_ROLL_PTR
points to index entry, index entry points to actual record (originalDB_ROLL_PTR
value). It must be possible to figure out first index entry (and header) fromDB_ROLL_PTR
of any record.DB_ROLL_PTR
to respect undo index.DATA_ROLL_PTR
code invasion: 22.row_vers_build_for_consistent_read()
.Search criteria:
view->changes_visible(i) && !view->changes_visible(i-1)
, wherei
is index from undo index.Local undo index as alternative
Scan undo records in
row_vers_build_for_consistent_read()
withouttrx_undo_prev_version_build()
, build temporary undo index. Then do binary search. This avoids copying of whole records in linear scan.This is much easier to implement than permanent undo index and it can be used as first stage of development.
References
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