Created
February 20, 2020 09:42
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#!/bin/sh | |
# Flush MySQL tables to the disk before the filesystem is frozen. | |
# At the same time, this keeps a read lock in order to avoid write accesses | |
# from the other clients until the filesystem is thawed. | |
MYSQL="/usr/bin/mysql" | |
MYSQL_OPTS="-uroot" #"-prootpassword" | |
FIFO=/var/run/mysql-flush.fifo | |
# Check mysql is installed and the server running | |
[ -x "$MYSQL" ] && "$MYSQL" $MYSQL_OPTS < /dev/null || exit 0 | |
flush_and_wait() { | |
printf "FLUSH TABLES WITH READ LOCK \\G\n" | |
trap 'printf "$(date): $0 is killed\n">&2' HUP INT QUIT ALRM TERM | |
read < $FIFO | |
printf "UNLOCK TABLES \\G\n" | |
rm -f $FIFO | |
} | |
case "$1" in | |
freeze) | |
mkfifo $FIFO || exit 1 | |
flush_and_wait | "$MYSQL" $MYSQL_OPTS & | |
# wait until every block is flushed | |
while [ "$(echo 'SHOW STATUS LIKE "Key_blocks_not_flushed"' |\ | |
"$MYSQL" $MYSQL_OPTS | tail -1 | cut -f 2)" -gt 0 ]; do | |
sleep 1 | |
done | |
# for InnoDB, wait until every log is flushed | |
INNODB_STATUS=$(mktemp /tmp/mysql-flush.XXXXXX) | |
[ $? -ne 0 ] && exit 2 | |
trap "rm -f $INNODB_STATUS; exit 1" HUP INT QUIT ALRM TERM | |
while :; do | |
printf "SHOW ENGINE INNODB STATUS \\G" |\ | |
"$MYSQL" $MYSQL_OPTS > $INNODB_STATUS | |
LOG_CURRENT=$(grep 'Log sequence number' $INNODB_STATUS |\ | |
tr -s ' ' | cut -d' ' -f4) | |
LOG_FLUSHED=$(grep 'Log flushed up to' $INNODB_STATUS |\ | |
tr -s ' ' | cut -d' ' -f5) | |
[ "$LOG_CURRENT" = "$LOG_FLUSHED" ] && break | |
sleep 1 | |
done | |
rm -f $INNODB_STATUS | |
;; | |
thaw) | |
[ ! -p $FIFO ] && exit 1 | |
echo > $FIFO | |
;; | |
*) | |
exit 1 | |
;; | |
esac |
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