syncer: improve performance - part 2

[csuzhangxc]

What problem does this PR solve?

improve binlog replication performance in some cases.

What is changed and how it works?

• do not use null value as the concurrence dispatch key
• decrease default value of queue-size from 5120 to 1024
• add checkpoint-flush-interval config item
• update binlogSkippedEventsTotal to skipBinlogDurationHistogram to support observe duration and update the Grafana dashboard

Check List

Tests

• Unit test
• Integration test

Code changes

• Has exported variable/fields change
• Has persistent data change

Side effects

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

Related changes

• Need to update the documentation
• Need to update the dm/dm-ansible
• Need to be included in the release note

[codecov]

Codecov Report

Merging #597 into release-1.0 will decrease coverage by 0.0086%.
The diff coverage is 89.4736%.

@@                 Coverage Diff                 @@
##           release-1.0       #597        +/-   ##
===================================================
- Coverage      57.2752%   57.2665%   -0.0087%     
===================================================
  Files              161        161                
  Lines            16721      16741        +20     
===================================================
+ Hits              9577       9587        +10     
- Misses            6200       6206         +6     
- Partials           944        948         +4     

[csuzhangxc]

/run-all-tests

[csuzhangxc]

@WangXiangUSTC @lichunzhu PTAL

[WangXiangUSTC]

seems that we have too many debug log, if we are debug other issue and need to enable debug log, these logs may disturb us.

rest LGTM

[csuzhangxc]

seems that we have too many debug log, if we are debug other issue and need to enable debug log, these logs may disturb us.

@WangXiangUSTC

em... but these logs are still needed for debug (or just let them as the placeholder). maybe when debugging, we can choose to?

1. change some of them to info or higher
2. do not run with debug too long

[lichunzhu]

LGTM

[WangXiangUSTC]

seems that we have too many debug log, if we are debug other issue and need to enable debug log, these logs may disturb us.

em... but these logs are still needed for debug (or just let them as the placeholder). maybe when debugging, we can choose to?

1. change some of them to info or higher
2. do not run with debug too long

OK，LGTM