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I'm trying to drop a table on a local mysql instance, and the DROP statement (DROP TABLE wqs_info) hangs out forever...

Looking at mysql logs, I see the lock dumps:

--Thread 18692 has waited at btr0cur.cc line 1870 for 241.00 seconds the semaphore:
X-lock (wait_ex) on RW-latch at 00000194D3745E88 created in file buf0buf.cc line 1460
a writer (thread id 18692) has reserved it in mode  wait exclusive
number of readers 1, waiters flag 1, lock_word: efffffff
Last time read locked in file row0row.cc line 989
Last time write locked in file g:\ade\build\sb_0-26514852-1514435511.83\mysql-5.7.21\storage\innobase\include\mtr0mtr.ic line 117

What's strange here is that thread 18692 (a mysqld thread) is waiting for a lock that it's already owning?! How can this be possible?

(after 4-5 server restarts, I finally managed to drop the table, but I want to know how it's possible for a thread to wait for a lock itself owns?!)

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  • What version of mysql?
    – Rick James
    Nov 20, 2019 at 19:36
  • @RickJames 5.7.21 (on windows)
    – Xenos
    Nov 20, 2019 at 19:49

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