Consider both memory free proportion and absolute value before blocking.

See around

if float64(memory.Available) / float64(memory.Total) < 0.2 {
	if i % 30 == 0 { // suppress log
		b.logger.Warn("memory is less than 20%. pause parsing binlog for 1s",
			"available", memory.Available, "total", memory.Total)

[asiroliu]

VM: 2 cpu 8GB memory
OS: CentOS 7.5.1804
Tool: yum install stress

verify:

1. deploy DTLE
2. run stress make memory free more than 1GB and less than 1.6GB

shell> stress --vm 6 --vm-bytes 1G --vm-hang 30

shell> free -h
              total        used        free      shared  buff/cache   available
Mem:           7.8G        6.6G        1.2G         16M        1.1G        1.2G
Swap:            0B          0B          0B

4. check dtle log, should not print log pause parsing binlog for 1s
5. run stress make memory free less than 1GB

shell> stress --vm 7 --vm-bytes 1G --vm-hang 30

shell> free -h
              total        used        free      shared  buff/cache   available
Mem:           7.8G        7.6G        262M         16M        235M       263M
Swap:            0B          0B          0B

6. check dtle log

2021-04-02T06:18:59.632Z [WARN]  client.driver_mgr.dtle: memory is less than 20% and 1GiB. pause parsing binlog for 1s: driver=dtle job=test1 total=3.97406208e+09 @module=reader available=2.76373504e+08 timestamp=2021-04-02T06:18:59.632Z
2021-04-02T06:19:29.632Z [INFO]  client.driver_mgr.dtle: memory is greater than 20%. continue parsing binlog: driver=dtle total=3.97406208e+09 @module=reader available=9.12072704e+08 job=test1 timestamp=2021-04-02T06:19:29.632Z
2021-04-02T06:19:30.632Z [WARN]  client.driver_mgr.dtle: memory is less than 20% and 1GiB. pause parsing binlog for 1s: driver=dtle @module=reader available=2.7625472e+08 job=test1 total=3.97406208e+09 timestamp=2021-04-02T06:19:30.632Z
2021-04-02T06:20:00.632Z [WARN]  client.driver_mgr.dtle: memory is less than 20% and 1GiB. pause parsing binlog for 1s: driver=dtle @module=reader available=2.99491328e+08 job=test1 total=3.97406208e+09 timestamp=2021-04-02T06:20:00.631Z
2021-04-02T06:20:05.632Z [INFO]  client.driver_mgr.dtle: memory is greater than 20%. continue parsing binlog: driver=dtle @module=reader available=3.502727168e+09 job=test1 total=3.97406208e+09 timestamp=2021-04-02T06:20:05.632Z