And to answer zsolt's question, temp tablespace Pool expansion and the tablespace types in Pool has no relation to whether a tablespace is encrypted or not.

There was a question from on how the pool would look like when innodb_encrypt_tables is changed ON to OFF and OFF to ON dynamically?

Few points to keep in mind

1. if innodb_temp_tablespace_encrypt is ON, innodb_encrypt_tables is irrelevant. Session will always get encrypted session temp tablespace

2. if innodb_temp_tablespace_encrypt is OFF, innodb_encrypt_table value matters. innodb_encrypt_tables = OFF ? unencrypted session temp tablespace else encrypted session temp tablespace (ON/FORCE)

3. All tablespaces in session temporary tablespace pool are always unencrypted.

4. A session can have max 4 types of tablespace attached
   INTRINSIC, USER, "INSTRINSIC ENCRYPTED", "USER ENCRYPTED"

5. A session can have all these four types attached

How sessions get encrypted temp tablespace from a unencrypted session temp tablespace pool?

As noted above, all tablespace in session temp tabelspace pool are unencrypted. When a session request a tablespace, it first check if there is encrypted tablespace attached already. If so, it will use that.

IF an encrypted tablespace is not attached, it will get an unencrypted tablespace from pool and encrypts it (write encryption headers). All further writes to this tablespace will be encrypted.

How an encrypted temp tablespace from session return to a pool of unencrypted tablespaces?

On session disconnect, temp tablespace is truncated and recreated. So the tablespace is unencrypted now and returned to pool.

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