infoschema: support define decimal for virtual table in information_schema

[lonng]

Signed-off-by: Lonng heng@lonng.org

What problem does this PR solve?

This PR changes the columnInfo definition in the infoschema package and add a field decimal to this struct because some table needs to define the decimal of value.

And this PR delete the unuseful field elems.

What is changed and how it works?

1. Add a field decimal for struct columnInfo.
2. Use field initializer for columnInfo and delete the fields which have default value.

Check List

Tests

• Unit test

Before this PR

| read-link | localhost:20180 | tikv_grpc_req_batch_size               |                                         |     0.99 |     1.8159727508612207 |      1.6320000000000003 |     1.9061904761904764 |
| read-link | localhost:20180 | tikv_grpc_resp_batch_size              |                                         |     0.99 |     1.7700137961869462 |      1.4650000000000096 |     1.8888888888888888 |
| read-link | localhost:10080 | tidb_cop_duration                      |                                         |     0.99 |   0.007507018735744536 |   0.0022799999999999878 |   0.051039999999999905 |
| read-link | localhost:20180 | tikv_cop_wait_duration                 | index                                   |     0.99 |   0.005916703859976283 |   0.0009855882352941177 |     0.0486400000000001 |
| read-link | localhost:20180 | tikv_cop_wait_duration                 | select                                  |     0.99 |  0.0025532449039733186 |             0.000976875 |   0.013040000000000013 |
| read-link | localhost:20180 | tikv_cop_handle_duration               | index                                   |     0.99 |   0.000981563954059329 |   0.0009705555555555557 |  0.0009883333333333335 |
| read-link | localhost:20180 | tikv_cop_handle_duration               | select                                  |     0.99 |  0.0009825811178332529 |   0.0009549999999999999 |                0.00099 |
| read-link | localhost:20180 | tikv_cop_kv_cursor_operations          | index                                   |     0.99 |     1.9666665041947302 |       1.962666666666667 |     1.9700000000000002 |
| read-link | localhost:20180 | tikv_cop_kv_cursor_operations          | select                                  |     0.99 |     2.3957500729820453 |                1.973125 |                   6.48 |
| read-link | localhost:20180 | tikv_cop_request_duration              | index                                   |     0.99 |   0.006183691322898403 |   0.0009924193548387097 |     0.0486400000000001 |
| read-link | localhost:20180 | tikv_cop_request_duration              | select                                  |     0.99 |   0.002799206018446358 |    0.000990263157894737 |   0.013040000000000013 |
| read-link | localhost:20180 | tikv_cop_request_durations             | index                                   |     NULL |     1.0565660570594855 |     0.13333037043621251 |     1.2444997555446908 |
| read-link | localhost:20180 | tikv_cop_request_durations             | select                                  |     NULL |     0.8133076072877152 |     0.13333629636214137 |     1.0000444464198408 |

After this PR

| read-link | localhost:20180 | tikv_cop_total_kv_cursor_operations    | select                                  |     NULL |      1.000767 |      0.933333 |      1.066785 |
| read-link | localhost:20180 | tikv_cop_total_requests                | index                                   |     NULL |      1.005068 |      0.933375 |      1.066785 |
| read-link | localhost:20180 | tikv_cop_total_requests                | select                                  |     NULL |      0.737671 |      0.688889 |      0.800036 |
| read-link | localhost:20180 | tikv_cop_total_response_size           |                                         |     NULL |    147.697741 |    147.390174 |    150.416713 |
| read-link | localhost:20180 | tikv_cop_total_rocksdb_perf_statistics | index, block_cache_hit_count            |     NULL |      3.014488 |      2.822348 |      3.200142 |
| read-link | localhost:20180 | tikv_cop_total_rocksdb_perf_statistics | index, block_read_byte                  |     NULL |      0.000000 |      0.000000 |      0.000000 |
| read-link | localhost:20180 | tikv_cop_total_rocksdb_perf_statistics | index, block_read_count                 |     NULL |      0.000000 |      0.000000 |      0.000000 |
| read-link | localhost:20180 | tikv_cop_total_rocksdb_perf_statistics | index, internal_delete_skipped_count    |     NULL |      0.000000 |      0.000000 |      0.000000 |
| read-link | localhost:20180 | tikv_cop_total_rocksdb_perf_statistics | index, internal_key_skipped_count       |     NULL |      1.006502 |      0.911152 |      1.133384 |
| read-link | localhost:20180 | tikv_cop_total_rocksdb_perf_statistics | select, block_cache_hit_count           |     NULL |      2.148495 |      2.000000 |      2.355660 |
| read-link | localhost:20180 | tikv_cop_total_rocksdb_perf_statistics | select, block_read_byte                 |     NULL |      0.000000 |      0.000000 |      0.000000 |
| read-link | localhost:20180 | tikv_cop_total_rocksdb_perf_statistics | select, block_read_count                |     NULL |      0.000000 |      0.000000 |      0.000000 |

Release note

• No need.

[lonng]

/run-all-tests

[crazycs520]

LGTM

[tiancaiamao]

LGTM

[lonng]

/merge

[sre-bot]

/run-all-tests

[lonng]

/rebuild