# 表结构和表数据
CREATE TABLE `tab1` (
  `id` bigint unsigned NOT NULL AUTO_INCREMENT,
  `value` int NOT NULL,
  `status` tinyint unsigned NOT NULL DEFAULT '1',
  PRIMARY KEY (`id`),
  KEY `idx_value` (`value`)
);
insert into tab1 (value) values (5);
insert into tab1 (value) values (10);




#seesion 1:
begin;
update `tab1` set `status` = 3 where (`value` = 10);




#session 2:
update `tab1` set `status` = 3 where (`value` >= 4) and (`value` < 6); #阻塞

ICP_RESULT row_search_idx_cond_check(
    byte *mysql_rec,          *!< out: record
                              in MySQL format (invalid unless
                              prebuilt->idx_cond == true and
                              we return ICP_MATCH) */
    row_prebuilt_t *prebuilt, *!< in/out: prebuilt struct
                              for the table handle */
    const rec_t *rec,         *!< in: InnoDB record */
    const ulint *offsets)     *!< in: rec_get_offsets() */
{
  ICP_RESULT result;
  ulint i;


  ut_ad(rec_offs_validate(rec, prebuilt->index, offsets));


  if (!prebuilt->idx_cond) {  如果index condition pushdown了，prebuilt->idx_cond为true，这里end_range并没有下推，所以这里直接返回了
    return (ICP_MATCH);
  }


  MONITOR_INC(MONITOR_ICP_ATTEMPTS);


  * Convert to MySQL format those fields that are needed for
  evaluating the index condition. */


  if (prebuilt->blob_heap != nullptr) {
    mem_heap_empty(prebuilt->blob_heap);
  }


  for (i = 0; i < prebuilt->idx_cond_n_cols; i++) {
    const mysql_row_templ_t *templ = &prebuilt->mysql_template[i];


    * Skip virtual columns */
    if (templ->is_virtual) {
      continue;
    }


    if (!row_sel_store_mysql_field(
            mysql_rec, prebuilt, rec, prebuilt->index, prebuilt->index, offsets,
            templ->icp_rec_field_no, templ, ULINT_UNDEFINED, nullptr,
            prebuilt->blob_heap)) {
      return (ICP_NO_MATCH);
    }
  }


  * We assume that the index conditions on
  case-insensitive columns are case-insensitive. The
  case of such columns may be wrong in a secondary
  index, if the case of the column has been updated in
  the past, or a record has been deleted and a record
  inserted in a different case. */
  result = innobase_index_cond(prebuilt->m_mysql_handler);  通过该函数去判断记录是否满足下推条件
  switch (result) {
    case ICP_MATCH:
      * Convert the remaining fields to MySQL format.
      If this is a secondary index record, we must defer
      this until we have fetched the clustered index record. */
      if (!prebuilt->need_to_access_clustered ||
          prebuilt->index->is_clustered()) {
        if (!row_sel_store_mysql_rec(mysql_rec, prebuilt, rec, nullptr, FALSE,
                                     prebuilt->index, prebuilt->index, offsets,
                                     false, nullptr, prebuilt->blob_heap)) {
          ut_ad(prebuilt->index->is_clustered());
          return (ICP_NO_MATCH);
        }
      }
      MONITOR_INC(MONITOR_ICP_MATCH);
      return (result);
    case ICP_NO_MATCH:
      MONITOR_INC(MONITOR_ICP_NO_MATCH);
      return (result);
    case ICP_OUT_OF_RANGE:
      MONITOR_INC(MONITOR_ICP_OUT_OF_RANGE);
      const auto record_buffer = row_sel_get_record_buffer(prebuilt);
      if (record_buffer) {
        record_buffer->set_out_of_range(true);
      }
      return (result);
  }


  ut_error;
  return (result);
}

if (compare_key(end_range) > 0) {


      /*


        The last read row does not fall in the range. So request


        storage engine to release row lock if possible.


      */


      unlock_row(); // 这里最终会调用row_unlock_for_mysql函数放掉刚刚在 sel_set_rec_lock 加上的锁。


      result = HA_ERR_END_OF_FILE;


}

# 表结构和表数据
CREATE TABLE `tab1` (
`id` bigint unsigned NOT NULL,
`value` int NOT NULL DEFAULT 0,
`status` tinyint unsigned NOT NULL DEFAULT '1',
PRIMARY KEY (`id`)
);
insert into tab1 (id) values (5);
insert into tab1 (id) values (10);




#seesion 1:
begin;
select * from `tab1` where (`id` = 10) for update;




#session 2:
select * from `tab1` where (`id` >= 4) and (`id` < 6) for update; #阻塞

# 表结构和表数据
CREATE TABLE `tab1` (
`id` bigint unsigned NOT NULL,
`value` int NOT NULL DEFAULT 0,
`status` tinyint unsigned NOT NULL DEFAULT '1',
PRIMARY KEY (`id`)
);
insert into tab1 (id) values (5);
insert into tab1 (id) values (10);




#seesion 1:
begin;
update `tab1` set `status` = 3 where (`id` = 10);




#session 2:
update `tab1` set `status` = 3 where (`id` >= 4) and (`id` < 6); #不会阻塞