[PLAN] Reconsider auto_create_table option because it is not intuitive

[sonots]

PROBLEM

auto_create_table: true option is not intuitive because, tables are automatically created in serveral modes such as replace even if auto_create_table: false (default).

This is because it is mandatory to create a new table with mode: replace because it works like

• create a temp table (HERE)
• load data into a temp table
• copy the temp table to the target table atomically. (or HERE)
• delete the temp table

BACKGROUND REASON

This plugin has behaved like this from old days, when this plugin was java implementation.

I guess (I am not the original author) this is because

• auto_create_table: false is the default value
• raising error with mode: replace under a default configuration feels bad

IDEA

Change the default value to something like auto_create_table: 'auto'?

And, then, raise an error with contradictory configuration such as

• mode: replace and auto_create_table: false
• mode: delete_in_advance and auto_create_table: false
• TODO: write completed list

ANOTHER PROBLEM

For partitioned table #58, mode: replace copy tables into a partition rather than a table.
Thus, it does not create a table. It requires that a table already exists.

auto_create_table: true or false works to create a table this case as its word describes.
It is not mandatory to create a new table with mode: replace for a partitioned table.

CONCLUSION

So...?

[sonots]

Let me change as following simply:

• auto_create_table: false is available only for mode: append_direct
• Other modes requires auto_create_table: true
• Change the default value of auto_create_table to true.
• Drop support of auto_create_table: false for creating a partition (with partitioning decorator)

This is based on my assumption that

• there are few people using mode: append_direct
• there are few people creating a table with partitioning decorator (because we can use field partitioning now) together with auto_create_table: false
• Most of people using replace mode with the previous behavior which always creates a temp table automatically