[DISCUSS] Change some default config values of

Hi dev & users,

We propose to change some default values of blocking shuffle to improve the user out-of-box experience (not influence streaming). The default values we want to change are as follows:

1. Data compression (taskmanager.network.blocking-shuffle.compression.enabled): Currently, the default value is 'false'. Usually, data compression can reduce both disk and network IO which is good for performance. At the same time, it can save storage space. We propose to change the default value to true.

2. Default shuffle implementation (taskmanager.network.sort-shuffle.min-parallelism): Currently, the default value is 'Integer.MAX', which means by default, Flink jobs will always use hash-shuffle. In fact, for high parallelism, sort-shuffle is better for both stability and performance. So we propose to reduce the default value to a proper smaller one, for example, 128. (We tested 128, 256, 512 and 1024 with a tpc-ds and 128 is the best one.)

3. Read buffer of sort-shuffle (taskmanager.memory.framework.off-heap.batch-shuffle.size): Currently, the default value is '32M'. Previously, when choosing the default value, both ‘32M' and '64M' are OK for tests and we chose the smaller one in a cautious way. However, recently, it is reported in the mailing list that the default value is not enough which caused a buffer request timeout issue. We already created a ticket to improve the behavior. At the same time, we propose to increase this default value to '64M' which can also help.

4. Sort buffer size of sort-shuffle (taskmanager.network.sort-shuffle.min-buffers): Currently, the default value is '64' which means '64' network buffers (32k per buffer by default). This default value is quite modest and the performance can be influenced. We propose to increase this value to a larger one, for example, 512 (the default TM and network buffer configuration can serve more than 10 result partitions concurrently).

We already tested these default values together with tpc-ds benchmark in a cluster and both the performance and stability improved a lot. These changes can help to improve the out-of-box experience of blocking shuffle. What do you think about these changes? Is there any concern? If there are no objections, I will make these changes soon. *来自志愿者整理的flink