How long can a TICDC synchronization task be paused?

This topic has been translated from a Chinese forum by GPT and might contain errors.

Original topic: TICDC的同步任务可以暂停多长时间?

| username: TiDBer_5VobY5Th

After using OpenAPI to call the pause synchronization task
POST /api/v2/changefeeds/{changefeed_id}/pause

How long can this synchronization task be paused? For example, if the database continues to have data changes, will it fill up the cache or disk?

| username: 这里介绍不了我 | Original post link

  1. How long can the synchronization task be paused?
    This depends on your source-side GC time. If your historical versions are cleaned up, naturally the task cannot be restarted.

  2. For example, if the database is constantly changing, will it fill up the cache or disk?
    TiCDC needs disk space mainly to buffer data that accumulates when the downstream consumption is not timely during upstream write peaks. During normal operation, it will require writing to the disk, but it usually does not become a bottleneck for synchronization throughput and latency. The impact of writing to the disk on latency is within hundreds of milliseconds. Moreover, TiCDC officially recommends an SSD with 500GB+ capacity.

| username: zhaokede | Original post link

This depends on how long you can tolerate data inconsistency in your business. Additionally, it depends on whether resources are sufficient.

| username: yiduoyunQ | Original post link

| username: zhanggame1 | Original post link

As long as there is no garbage collection (GC), it can stop for as long as it wants, it’s just occupying disk space.

| username: FutureDB | Original post link

That’s right. If it stops for too long and GC occurs, you can only reinitialize a set of data offline to the downstream, keep the data consistent between upstream and downstream, and then create a new changefeed task.

| username: TiDBer_小阿飞 | Original post link

According to the principle of TiCDC, TiCDC monitors the information of each Region Raft Log in the upstream TiKV in real-time and generates corresponding data change information with multiple SQL statements based on the differences before and after each transaction. Therefore, it depends on how long the information of the Region Raft Log can be retained.

| username: MrSylar | Original post link

Determined by tidb_gc_life_time and tidb_gc_max_wait_time, with a default value of 24 hours.

| username: Daniel-W | Original post link

Do not exceed the gc ttl time configured in cdc.

| username: yytest | Original post link

Limit memory usage: When calling the interface to pause synchronization tasks, you can specify a parameter to limit memory usage. When memory usage reaches this limit, the synchronization task will automatically stop to avoid memory overflow.
Regularly check memory and disk usage: During the pause of synchronization tasks, regularly check memory and disk usage to ensure they do not exceed limits. If memory or disk usage is found to be approaching the limit, measures can be taken, such as clearing memory or increasing disk space.
Set a timeout for synchronization tasks: When calling the interface to pause synchronization tasks, you can specify a timeout. When the pause time of the synchronization task exceeds this timeout, the synchronization task will automatically resume. This way, even if memory and disk space are sufficient, you can avoid the synchronization task being paused for too long.