sync-diff-inspector: Use md5 func replace crc32 for checksum

[erwadba]

What problem does this PR solve?

Issue Number: close #703 #634

What is changed and how it works?

Use md5 func replace crc32 for checksum.Data check is more accurate.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation
• Need to be included in the release note

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[erwadba]

@lance6716 @Leavrth PTAL,tks.

[lance6716]

Hi, I think MD5 is much slower than CRC32, can you test about thier performance?

[Leavrth]

😭 Unfortunately, it will take twice as long.
Currently TiDB hasn't optimized this kind of SQL. The sub expression MD5(CONCAT_WS(',', %s, CONCAT(%s))) will be calculated twice.
pingcap/tidb#39576

[erwadba]

Hi, I think MD5 is much slower than CRC32, can you test about thier performance?

I use sync-diff-inspector check 2T data in my production environment.
source tidb v6.5
target tidb v6.5
CRC32
Time Cost: 34m38.359171205s
Average Speed: 327.637020MB/s
MD5
Time Cost: 40m9.020688748s
Average Speed: 282.645290MB/s

[Leavrth]

Hi, I think MD5 is much slower than CRC32, can you test about thier performance?

I use sync-diff-inspector check 2T data in my production environment. source tidb v6.5 target tidb v6.5 CRC32 Time Cost: 34m38.359171205s Average Speed: 327.637020MB/s MD5 Time Cost: 40m9.020688748s Average Speed: 282.645290MB/s

How many are columns of the test tables? It shows that the speed of CRC32 is close to that of MD5.
However, please refer to this comment #707 (comment), I think if the columns of the test table become more and more, the speed gap will be widen.

[erwadba]

How many are columns of the test tables? It shows that the speed of CRC32 is close to that of MD5.

There are 93 tables. The small one has 5 columns and the big one has 25 columns.
Maybe we can use md5 checksum like this.
https://www.percona.com/blog/how-to-avoid-hash-collisions-when-using-mysqls-crc32-function/

use test;
create table f1(id int primary key,f float);
insert into f1 values(1,0.1),(2,0.01),(3,0.001);
SELECT COUNT(*) as CNT, BIT_XOR(CAST(CONV(SUBSTRING(@crc, 1, 16), 16, 10) AS UNSIGNED)) LMD5, BIT_XOR(CAST(CONV(SUBSTRING(@crc :=MD5(CONCAT_WS(',',`id`, `f`, CONCAT(ISNULL(`id`), ISNULL(`f`)))), 17, 16), 16, 10) AS UNSIGNED)) RMD5  FROM `test`.`f1` WHERE ((TRUE) AND (TRUE));

[Leavrth]

How many are columns of the test tables? It shows that the speed of CRC32 is close to that of MD5.

There are 93 tables. The small one has 5 columns and the big one has 25 columns. Maybe we can use md5 checksum like this. https://www.percona.com/blog/how-to-avoid-hash-collisions-when-using-mysqls-crc32-function/

use test;
create table f1(id int primary key,f float);
insert into f1 values(1,0.1),(2,0.01),(3,0.001);
SELECT COUNT(*) as CNT, BIT_XOR(CAST(CONV(SUBSTRING(@crc, 1, 16), 16, 10) AS UNSIGNED)) LMD5, BIT_XOR(CAST(CONV(SUBSTRING(@crc :=MD5(CONCAT_WS(',',`id`, `f`, CONCAT(ISNULL(`id`), ISNULL(`f`)))), 17, 16), 16, 10) AS UNSIGNED)) RMD5  FROM `test`.`f1` WHERE ((TRUE) AND (TRUE));

mysql> SELECT COUNT(1) AS CNT, BIT_XOR(CAST(CRC32(CONCAT_WS(',', `s_i_id`, `s_w_id`, `s_quantity`, `s_dist_01`, `s_dist_02`, `s_dist_03`, `s_dist_04`, `s_dist_05`, `s_dist_06`, `s_dist_07`, `s_dist_08`, `s_dist_09`, `s_dist_10`, `s_ytd`, `s_order_cnt`, `s_remote_cnt`, `s_data`, CONCAT(ISNULL(`s_i_id`), ISNULL(`s_w_id`))))AS UNSIGNED)) as BIT_XOR_CHECKSUM FROM test.stock;
+----------+------------------+
| CNT      | BIT_XOR_CHECKSUM |
+----------+------------------+
| 12800000 |        385643470 |
+----------+------------------+
1 row in set (5.97 sec)

mysql> SELECT COUNT(1) as CNT, BIT_XOR(CAST(CONV(SUBSTRING(@crc, 1, 16), 16, 10) AS UNSIGNED)) LMD5, BIT_XOR(CAST(CONV(SUBSTRING(@crc :=MD5(CONCAT_WS(',', `s_i_id`, `s_w_id`, `s_quantity`, `s_dist_01`, `s_dist_02`, `s_dist_03`, `s_dist_04`, `s_dist_05`, `s_dist_06`, `s_dist_07`, `s_dist_08`, `s_dist_09`, `s_dist_10`, `s_ytd`, `s_order_cnt`, `s_remote_cnt`, `s_data`, CONCAT(ISNULL(`s_i_id`), ISNULL(`s_w_id`)))), 17, 16), 16, 10) AS UNSIGNED)) RMD5  FROM `test`.`stock` WHERE ((TRUE) AND (TRUE));
+----------+----------------------+----------------------+
| CNT      | LMD5                 | RMD5                 |
+----------+----------------------+----------------------+
| 12800000 | 17055727021754144759 | 17409312425610765406 |
+----------+----------------------+----------------------+
1 row in set (1 min 37.94 sec)

mysql> SELECT COUNT(1) as CNT, BIT_XOR(CAST(CONV(SUBSTRING(MD5(CONCAT_WS(',', `s_i_id`, `s_w_id`, `s_quantity`, `s_dist_01`, `s_dist_02`, `s_dist_03`, `s_dist_04`, `s_dist_05`, `s_dist_06`, `s_dist_07`, `s_dist_08`, `s_dist_09`, `s_dist_10`, `s_ytd`, `s_order_cnt`, `s_remote_cnt`, `s_data`, CONCAT(ISNULL(`s_i_id`), ISNULL(`s_w_id`)))), 1, 16), 16, 10) AS UNSIGNED)) LMD5, BIT_XOR(CAST(CONV(SUBSTRING(MD5(CONCAT_WS(',', `s_i_id`, `s_w_id`, `s_quantity`, `s_dist_01`, `s_dist_02`, `s_dist_03`, `s_dist_04`, `s_dist_05`, `s_dist_06`, `s_dist_07`, `s_dist_08`, `s_dist_09`, `s_dist_10`, `s_ytd`, `s_order_cnt`, `s_remote_cnt`, `s_data`, CONCAT(ISNULL(`s_i_id`), ISNULL(`s_w_id`)))), 17, 16), 16, 10) AS UNSIGNED)) RMD5  FROM `test`.`stock` WHERE ((TRUE) AND (TRUE));
+----------+----------------------+----------------------+
| CNT      | LMD5                 | RMD5                 |
+----------+----------------------+----------------------+
| 12800000 | 18443984006065217657 | 17409312425610765406 |
+----------+----------------------+----------------------+
1 row in set (11.99 sec)

mysql> SELECT COUNT(1) as CNT, BIT_XOR(CAST(CONV(SUBSTRING(MD5(CONCAT_WS(',', `s_i_id`, `s_w_id`, `s_quantity`, `s_dist_01`, `s_dist_02`, `s_dist_03`, `s_dist_04`, `s_dist_05`, `s_dist_06`, `s_dist_07`, `s_dist_08`, `s_dist_09`, `s_dist_10`, `s_ytd`, `s_order_cnt`, `s_remote_cnt`, `s_data`, CONCAT(ISNULL(`s_i_id`), ISNULL(`s_w_id`)))), 1, 16), 16, 10) AS UNSIGNED)) LMD5 FROM `test`.`stock` WHERE ((TRUE) AND (TRUE));
+----------+----------------------+
| CNT      | LMD5                 |
+----------+----------------------+
| 12800000 | 18443984006065217657 |
+----------+----------------------+
1 row in set (7.52 sec)

If use @crc32, the calculation operation won't push down to TiKV. That the whole data is sent to TiDB from TiKV costs too hightly.

mysql> explain SELECT COUNT(1) as CNT, BIT_XOR(CAST(CONV(SUBSTRING(@crc, 1, 16), 16, 10) AS UNSIGNED)) LMD5, BIT_XOR(CAST(CONV(SUBSTRING(@crc :=MD5(CONCAT_WS(',', `s_i_id`, `s_w_id`, `s_quantity`, `s_dist_01`, `s_dist_02`, `s_dist_03`, `s_dist_04`, `s_dist_05`, `s_dist_06`, `s_dist_07`, `s_dist_08`, `s_dist_09`, `s_dist_10`, `s_ytd`, `s_order_cnt`, `s_remote_cnt`, `s_data`, CONCAT(ISNULL(`s_i_id`), ISNULL(`s_w_id`)))), 17, 16), 16, 10) AS UNSIGNED)) RMD5  FROM `test`.`stock` WHERE ((TRUE) AND (TRUE));
+----------------------------+-------------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| id                         | estRows     | task      | access object | operator info                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
+----------------------------+-------------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| HashAgg_6                  | 1.00        | root      |               | funcs:count(1)->Column#18, funcs:bit_xor(Column#21)->Column#19, funcs:bit_xor(Column#22)->Column#20                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| └─Projection_19            | 12800000.00 | root      |               | cast(conv(substring(getvar(crc), 1, 16), 16, 10), bigint(22) UNSIGNED BINARY)->Column#21, cast(conv(substring(setvar(crc, md5(concat_ws(,, cast(test.stock.s_i_id, var_string(20)), cast(test.stock.s_w_id, var_string(20)), cast(test.stock.s_quantity, var_string(20)), test.stock.s_dist_01, test.stock.s_dist_02, test.stock.s_dist_03, test.stock.s_dist_04, test.stock.s_dist_05, test.stock.s_dist_06, test.stock.s_dist_07, test.stock.s_dist_08, test.stock.s_dist_09, test.stock.s_dist_10, cast(test.stock.s_ytd, var_string(20)), cast(test.stock.s_order_cnt, var_string(20)), cast(test.stock.s_remote_cnt, var_string(20)), test.stock.s_data, 00))), 17, 16), 16, 10), bigint(22) UNSIGNED BINARY)->Column#22 |
|   └─TableReader_12         | 12800000.00 | root      |               | data:TableFullScan_11                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|     └─TableFullScan_11     | 12800000.00 | cop[tikv] | table:stock   | keep order:false                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
+----------------------------+-------------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
4 rows in set, 4 warnings (0.01 sec)

the data is generated by tiup bench tpcc prepare. Anyway, before this SQL is optimized by TiDB, it can only endure up to twice the time to exchange the accuracy of the result.

[Leavrth]

closed by #787