Обсуждение: Locking Tables & Backup Inquiry
I'm wanted to find out why is it recommended or even an option to lock tables during a backup of a database? I've never experimented with database backups so I'm only guessing it locks / freezes the data so no changes can be made while the backup is in process, correct? Just curious and wasn't able to find an answer online. My next question is more complex but more of a recommendations. I'm looking to see how do you guys backup your databases? Do you simply cron 'pg_dump' command line or do you have a script that gets called in cron using 'pg_dump' / 'pg_dumpall'? Just looking for ideas / recommendations for a simple / quick way to back up 5 small databases on my server.
On 12/14/2011 11:52 AM, Carlos Mennens wrote: > I'm wanted to find out why is it recommended or even an option to lock > tables during a backup of a database? I've never experimented with > database backups so I'm only guessing it locks / freezes the data so > no changes can be made while the backup is in process, correct? Just > curious and wasn't able to find an answer online. > > My next question is more complex but more of a recommendations. I'm > looking to see how do you guys backup your databases? Do you simply > cron 'pg_dump' command line or do you have a script that gets called > in cron using 'pg_dump' / 'pg_dumpall'? Just looking for ideas / > recommendations for a simple / quick way to back up 5 small databases > on my server. > I assume that is coming from a mysql world, where yes, locking is a good option. PG does not need it. Read up on MVCC. Your backup will "select * from table" and read it just fine. Other transactions can update/delete from the same table, but because of the magic of MVCC, the backup wont see em, and neither will be blocked. Meaning, your reads and writes dont block each other. Meaning, your app wont freeze while the backup runs. Yep, you simply cron a pg_dump. (dumpall if you want users/roles and all databases). No locking needed. -Andy
On Wed, Dec 14, 2011 at 1:15 PM, Andy Colson <andy@squeakycode.net> wrote: > Yep, you simply cron a pg_dump. (dumpall if you want users/roles and all > databases). No locking needed. So how would one put this in cron if I wanted to run this everyday? 0 * * * * /usr/bin/pg_dumpall > pg_dumpall.$DATE.sql Will that work above assuming I wanted to run this every day at that specific time? I'm just guessing since I've never created a Crontab or messed with PG backups.
On 12/14/2011 12:26 PM, Carlos Mennens wrote: > On Wed, Dec 14, 2011 at 1:15 PM, Andy Colson<andy@squeakycode.net> wrote: >> Yep, you simply cron a pg_dump. (dumpall if you want users/roles and all >> databases). No locking needed. > > So how would one put this in cron if I wanted to run this everyday? > > 0 * * * * /usr/bin/pg_dumpall> pg_dumpall.$DATE.sql > > Will that work above assuming I wanted to run this every day at that > specific time? I'm just guessing since I've never created a Crontab or > messed with PG backups. > google is your friend. this'll run every hour. > 0 * * * * /usr/bin/pg_dumpall> pg_dumpall.$DATE.sql try: 0 4 * * * /usr/bin/pg_dumpall> pg_dumpall.$DATE.sql that'll run at 4am every day. Watch the path's, who know's what directory is current: 0 4 * * * /usr/bin/pg_dumpall > /backup/pg_dumpall.$DATE.sql -Andy
On Wed, Dec 14, 2011 at 1:38 PM, Andy Colson <andy@squeakycode.net> wrote: > this'll run every hour. > >> 0 * * * * /usr/bin/pg_dumpall> pg_dumpall.$DATE.sql Thank you! > try: > > 0 4 * * * /usr/bin/pg_dumpall> pg_dumpall.$DATE.sql > > that'll run at 4am every day. When I run the command in my shell (not in Cron), I'm prompted for my login password. Should I change the permissions in pg_hba.conf and enable INHERIT grants on my user? Should I place this in who's Cron line? Postgres? Carlos? or Root? > > Watch the path's, who know's what directory is current: > > 0 4 * * * /usr/bin/pg_dumpall > /backup/pg_dumpall.$DATE.sql Yes, I always check my paths and use full paths rather than symbolic links.
On 12/14/2011 12:54 PM, Carlos Mennens wrote: > On Wed, Dec 14, 2011 at 1:38 PM, Andy Colson<andy@squeakycode.net> wrote: >> this'll run every hour. >> >>> 0 * * * * /usr/bin/pg_dumpall> pg_dumpall.$DATE.sql > > Thank you! > >> try: >> >> 0 4 * * * /usr/bin/pg_dumpall> pg_dumpall.$DATE.sql >> >> that'll run at 4am every day. > > When I run the command in my shell (not in Cron), I'm prompted for my > login password. Should I change the permissions in pg_hba.conf and > enable INHERIT grants on my user? Should I place this in who's Cron > line? Postgres? Carlos? or Root? >> >> Watch the path's, who know's what directory is current: >> >> 0 4 * * * /usr/bin/pg_dumpall> /backup/pg_dumpall.$DATE.sql > > Yes, I always check my paths and use full paths rather than symbolic links. > That's up to you I guess. Assuming the crontab is running as root, you could add a .pgpass to root's home, which should be secure enough. -Andy
Carlos Mennens wrote: >> 0 4 * * * /usr/bin/pg_dumpall> pg_dumpall.$DATE.sql >> >> that'll run at 4am every day. > When I run the command in my shell (not in Cron), I'm prompted for my > login password. Should I change the permissions in pg_hba.conf and > enable INHERIT grants on my user? Should I place this in who's Cron > line? Postgres? Carlos? or Root? I'd use the postgres user and allow "trust" authentication for that user on local connections in pg_hba.conf. No grants are required. If you have write activity during the backup and you need all data of a database to be consistent, consider using pg_dump's --serializable-deferrable flag. Yours, Laurenz Albe