What is the major disadvantage of 2PC protocol?

What is the major disadvantage of 2PC protocol? Define blocking problem in distributed database

Blocking problem – In case of coordinator failure, Two Phase Commit (2PC) protocol uses various ways to complete the transaction (to abort or commit). It can be done using the messages found in the log files of participating sites. If all the participating sites have <ready T> message and no other control messages (such as <abort T> or <commit T>) then all the active sites which are participating in that transaction have to wait for their transaction coordinator to recover. 

The transaction T can be aborted or committed only if the failed transaction coordinator is restarted/come alive. This situation is called blocking problem.

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Click - Two phase commit protocol in pictures