Extracted from CORE-6346, as it is likely an independent issue. Active wire compression causes periodic blocks in FB 3.0.6. I first noticed it when inserting large binary blobs and executing long ddl statements, but probably affects all TCP communication.

The blocks last for up to several minutes, during which there is no obvious server activity (minimum CPU/HDD/Network load), so it looks rather like a timeout. The process eventually resumes (no error message), but the problem repeates soon after (on another blob segment or ddl command).
  
To reproduce the problem, it it sufficient to try to insert a large file (say Firebird installation exe file) into a binary blob field when wire compression is active. In FB 3.0.5 it takes just a second, while in 3.0.6 it would now probably last tens of minutes.

Workaround is either to disable the wire compression or switch back to FB 3.0.5.