On Fri, 30 Aug 2019 at 04:18, test user <[email protected]>
wrote:
> B. Is there any method for determining lock transitions for connections?
> - Is there an API?
> - Would it be possible to use dtrace to instrument SQLite to detect
> lock transitions?
> - Where should I be looking?
>
On unix sqlite uses fcntl() with cmd=F_SETLK on specific byte locations to
acquire locks -- I'm not familiar with dtrace, but I've used strace + sed
to watch sqlite lock activity before. eg:
#!/bin/sh
PID=$1
replace() {
echo "s#F_SETLK, {type=F_$1, whence=SEEK_SET, start=$2, len=$3}#$4#"
}
strace -Ttt -ff -e trace=fcntl -p $PID 2>&1 |
sed \
-e "$(replace RDLCK 1073741824 1 acquireR{PENDING})" \
-e "$(replace RDLCK 1073741825 1 acquireR{RESERVED})" \
-e "$(replace RDLCK 1073741826 510 acquire{SHARED})" \
-e "$(replace WRLCK 1073741824 1 acquireW{PENDING})" \
-e "$(replace WRLCK 1073741825 1 acquireW{RESERVED})" \
-e "$(replace WRLCK 1073741826 510 acquire{EXCLUSIVE})" \
-e "$(replace UNLCK 1073741824 2 release{PENDING+RESERVED})" \
-e "$(replace UNLCK 1073741824 1 release{PENDING})" \
-e "$(replace UNLCK 1073741825 1 release{RESERVED})" \
-e "$(replace UNLCK 1073741826 510 release{SHARED/EXCLUSIVE})" \
-e "$(replace UNLCK 0 0 release{ALL})"
-Rowan
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