关于InnoDB事务的一个“诡异”现象：RR隔离级别下的幻读现象（补充）

row_search_for_mysql：    if(prebuilt->select_lock_type != LOCK_NONE) {//锁读，不会读取老版本    ……    }else{//一致性非锁定读         if (trx->isolation_level ==TRX_ISO_READ_UNCOMMITTED) {//脏读、幻读等                   nothing to do         }else if (index == clust_index){                 //检查该记录是否本事务可见         if(UNIV_LIKELY(srv_force_recovery < 5) &&!lock_clust_rec_cons_read_sees(rec, index, offsets, trx->read_view){                 rec_t*      old_vers;                 //不可见则找上一个版本                 err = row_sel_build_prev_vers_for_mysql( trx->read_view,clust_index,prebuilt, rec, &offsets, &heap,&old_vers,&mtr);                  //上一个版本没有这个记录，放弃                  if (old_vers == NULL) {                         /*The row did not exist yet in the read view */                         gotonext_rec;                  }                   rec =old_vers;         }    }}mysql_update-> rr_quick->QUICK_RANGE_SELECT::get_next->ha_innobase::multi_range_read_next-> DsMrr_impl::dsmrr_next->handler::multi_range_read_next->handler::read_range_first->handler::ha_index_read_map-> handler::index_read_map->ha_innobase::index_read-> row_search_for_mysqlmysql_update->handler::ha_update_row->a_innobase::update_row-> row_update_for_mysql-> row_upd_step