With bitcoind -regtest -wallet=w1 -wallet=w2 -debug, before:
BerkeleyEnvironment::Flush: Flush(true) BerkeleyEnvironment::Flush: Flushing wallet.dat (refcount = 0)... BerkeleyEnvironment::Flush: wallet.dat checkpoint BerkeleyEnvironment::Flush: wallet.dat detach BerkeleyEnvironment::Flush: wallet.dat closed BerkeleyEnvironment::Flush: Flush(true) took 23ms BerkeleyEnvironment::Flush: Flush(true) BerkeleyEnvironment::Flush: Flushing wallet.dat (refcount = 0)... BerkeleyEnvironment::Flush: wallet.dat checkpoint BerkeleyEnvironment::Flush: wallet.dat detach BerkeleyEnvironment::Flush: wallet.dat closed BerkeleyEnvironment::Flush: Flush(true) took 19ms
After:
BerkeleyEnvironment::Flush: [/Users/joao/Library/Application Support/Bitcoin/regtest/wallets/w1] Flush(true) BerkeleyEnvironment::Flush: Flushing wallet.dat (refcount = 0)... BerkeleyEnvironment::Flush: wallet.dat checkpoint BerkeleyEnvironment::Flush: wallet.dat detach BerkeleyEnvironment::Flush: wallet.dat closed BerkeleyEnvironment::Flush: Flush(true) took 23ms BerkeleyEnvironment::Flush: [/Users/joao/Library/Application Support/Bitcoin/regtest/wallets/w2] Flush(true) BerkeleyEnvironment::Flush: Flushing wallet.dat (refcount = 0)... BerkeleyEnvironment::Flush: wallet.dat checkpoint BerkeleyEnvironment::Flush: wallet.dat detach BerkeleyEnvironment::Flush: wallet.dat closed BerkeleyEnvironment::Flush: Flush(true) took 19ms
Backport of core PR14760:
https://github.com/bitcoin/bitcoin/pull/14760/files
Depends on D4885.