the infimum record can be a dummy target for temporary record locks.
Stores on the page infimum record the explicit locks of another record.
This function is used to store the lock state of a record when it is
updated and the size of the record changes in the update. The record
is moved in such an update, perhaps to another page. The infimum record
acts as a dummy carrier record, taking care of lock releases while the
actual record is being moved. */
void
lock_rec_store_on_page_infimum(
/*===========================*/
const buf_block_t* block, /*!< in: buffer block containing rec */
const rec_t* rec) /*!< in: record whose lock state
is stored on the infimum
record of the same page; lock
bits are reset on the
record */
/* Predicate lock always on INFIMUM (0) */
if (is_predicate_lock(mode)) {
rec_lock.n_bits = 8;
memset(&lock[1], 0x0, 1);
supremum上的锁
For the last interval, the next-key lock locks the gap above the largest value in the
index and the “supremum” pseudo-record having a value higher than any value actually
in the index. The supremum is not a real index record, so, in effect,
this next-key lock locks only the gap following the largest index value.
页在重组分裂的时候，也有处理infimum，supremum上的锁
https://dev.mysql.com/blog-archive/innodb-data-locking-part-2-5-locks-deeper-dive/
针对infimum的锁，经过测试，只要更新的字段长度改变，增加或减小，也是悲观更新，都会出发拷贝锁到 infimum，长度没有改变那么不会触发，那如果有并发的请求，update一个页中的多行记录，那怎么办？infimum这种拷贝也会出现争用
mysqld!lock_rec_store_on_page_infimum(buf_block_t const*, unsigned char const*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/lock/lock0lock.cc:3629) mysqld!btr_cur_pessimistic_update(unsigned long, btr_cur_t*, unsigned long**, mem_block_info_t**, mem_block_info_t*, big_rec_t**, upd_t*, unsigned long, que_thr_t*, unsigned long long, mtr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/btr/btr0cur.cc:4496) mysqld!row_upd_clust_rec(unsigned long, upd_node_t*, dict_index_t*, unsigned long*, mem_block_info_t**, que_thr_t*, mtr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0upd.cc:2703) mysqld!row_upd_clust_step(upd_node_t*, que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0upd.cc:2957) mysqld!row_upd(upd_node_t*, que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0upd.cc:3054) mysqld!row_upd_step(que_thr_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0upd.cc:3200) mysqld!row_update_for_mysql_using_upd_graph(unsigned char const*, row_prebuilt_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0mysql.cc:2582) mysqld!row_update_for_mysql(unsigned char const*, row_prebuilt_t*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/row/row0mysql.cc:2672) mysqld!ha_innobase::update_row(unsigned char const*, unsigned char*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/innobase/handler/ha_innodb.cc:8257) mysqld!handler::ha_update_row(unsigned char const*, unsigned char*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/handler.cc:8134) mysqld!mysql_update(THD*, List<Item>&, List<Item>&, unsigned long long, enum_duplicates, unsigned long long*, unsigned long long*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_update.cc:894) mysqld!Sql_cmd_update::try_single_table_update(THD*, bool*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_update.cc:2906) mysqld!Sql_cmd_update::execute(THD*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_update.cc:3037) mysqld!mysql_execute_command(THD*, bool) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_parse.cc:3616) mysqld!mysql_parse(THD*, Parser_state*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_parse.cc:5584) mysqld!dispatch_command(THD*, COM_DATA const*, enum_server_command) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_parse.cc:1491) mysqld!do_command(THD*) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/sql_parse.cc:1032) mysqld!::handle_connection(void *) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/sql/conn_handler/connection_handler_per_thread.cc:313) mysqld!::pfs_spawn_thread(void *) (/Users/xiaoyu.bai/Downloads/mysql-5.7.29/storage/perfschema/pfs.cc:2197) libsystem_pthread.dylib!_pthread_start (Unknown Source:0)
另外针对这种非原地更新的，走的是悲观更新，跟mysql内部更新主键一样，将旧的记录标记删除，然后在插入新的记录。
为什么针对唯一索引的范围 dml会锁下一个记录？
有兴趣学习源码的加群一起学习啊 QQ： 700072075
