如何使用TiFlash
简介
TiFlash 是 TiDB HTAP 形态的关键组件。开启TiFlash后可以更好的满足用户的分析型业务场景需求。
步骤一 开启TiFlash
详情页切换到 “TiFlash” 面板
点击 ‘开启TiFlash’ 按钮, 打开开启窗口
确认节点规格和费用后，点击立即购买
步骤二 按表构建TiFlash副本
构建TiFlash副本
ALTER TABLE table_name SET TIFLASH REPLICA count;
count 表示副本数，0 表示删除。count数不超过已开启TiFlash节点数。查看表同步进度
SELECT * FROM information_schema.tiflash_replica WHERE TABLE_SCHEMA = '<db_name>' and TABLE_NAME = '<table_name>';
查询结果中AVAILABLE 字段表示该表的 TiFlash 副本是否可用。1 代表可用，0 代表不可用。副本状态为可用之后就不再改变，如果通过 DDL 命令修改副本数则会重新计算同步进度。
PROGRESS 字段代表同步进度，在 0.0~1.0 之间，1 代表至少 1 个副本已经完成同步。步骤三 使用TiFlash
同步完成后，TiDB 优化器会自动根据代价估算选择是否使用 TiFlash 副本。具体有没有选择 TiFlash 副本，可以通过 desc 或 explain analyze 语句查看，例如：
desc select count(*) from test.t;
+--------------------------+---------+--------------+---------------+--------------------------------+
| id | estRows | task | access object | operator info |
+--------------------------+---------+--------------+---------------+--------------------------------+
| StreamAgg_9 | 1.00 | root | | funcs:count(1)->Column#4 |
| └─TableReader_17 | 1.00 | root | | data:TableFullScan_16 |
| └─TableFullScan_16 | 1.00 | cop[tiflash] | table:t | keep order:false, stats:pseudo |
+--------------------------+---------+--------------+---------------+--------------------------------+
3 rows in set (0.00 sec)explain analyze select count(*) from test.t;
+--------------------------+---------+---------+--------------+---------------+----------------------------------------------------------------------+--------------------------------+-----------+------+
| id | estRows | actRows | task | access object | execution info | operator info | memory | disk |
+--------------------------+---------+---------+--------------+---------------+----------------------------------------------------------------------+--------------------------------+-----------+------+
| StreamAgg_9 | 1.00 | 1 | root | | time:83.8372ms, loops:2 | funcs:count(1)->Column#4 | 372 Bytes | N/A |
| └─TableReader_17 | 1.00 | 1 | root | | time:83.7776ms, loops:2, rpc num: 1, rpc time:83.5701ms, proc keys:0 | data:TableFullScan_16 | 152 Bytes | N/A |
| └─TableFullScan_16 | 1.00 | 1 | cop[tiflash] | table:t | time:43ms, loops:1 | keep order:false, stats:pseudo | N/A | N/A |
+--------------------------+---------+---------+--------------+---------------+----------------------------------------------------------------------+--------------------------------+-----------+------+关闭TiFlash
关闭TiFlash副本
ALTER TABLE table_name SET TIFLASH REPLICA 0;关闭TiFlash服务
在“TiFlash”面板中点击 ‘关闭TiFlash’ 按钮即可关闭TiFlash服务
- 官方文档