So my problem I hope someone can help me with is the following:
There is a Master SQL Server that is huge and updates pretty much 24/7...
So locking that database for a dump is no option.
For that reason there is a 2nd server configured to be the slave server of the first instance, replicating every transaction of the binary log file.
The problem in question is how to backup this 2nd instance... Since it is a MariaDB Server it seems that snapshot replication is not possible and even if we were to create a cron for that, the tables would need to be locked for the time of the snapshot creation (DB is around 100GB+).
We thought of two slave servers replicating from that one master, one creating a snapshot every other hour (one e.g. every odd hour while the other does the same thing, just on the even hours).
Is there anyway to get this to work?
Would this approach even work? Since I am able to delay the transactions from the master for x seconds but how would I approach this?
Thank you all in advance for your suggestions and ideas.
Best regards,
TheSaltyOne.
Related
I have two databases in different servers - center_db on siglv01\sql2008 and center_db on sig\sql2008.
Can I restart replication without needing to reinitialize it? The connection dropped more than 3 days ago and is now too slow: so I want to start replication without a reinitialize.
Based on the brief conversation above, I don't think you can do this without a re-init. Specifically, the distribution database only keeps so many commands before it starts trimming. The default is 72 hours. If the last command delivered to all of your subscribers is older than that, the distribution database doesn't have what it needs to play forward all of the activity that has happened since then.
Your only hope would be if the distribution agent is still running (it knows when the above situation happens and will give you an error saying as much). If so, try to figure out why delivery is slow (troubleshoot this like any other "slow application"; replication isn't magic) and see if it can get caught up that way. Depending on how many commands are remain undelivered, it may be faster to just re-init.
I'm running Firebird 2.5 (and have also tried earlier versions) on Windows. Every day after 12:00PM running insert/update queries on one specific table hang, but complete successfully by 12:35 or so, no matter when started. It does seem that Firebird is doing some kind of maintenance on the table and it takes half an hour to complete, during which time the table cannot be written to (but the reads are fast). The table itself is really small, some 10000 rows, compared to millions of rows we have in other tables - and other tables do not get stuck.
I haven't been able to find any reason or solution. I tried dumping the table and restoring it, which didn't help, I tried switching between superserver and classic, changed versions with no success.
Has anyone experienced a problem like this?
No. Firebird doesn't have any internal maintenance procedures bind to some specified time of a day. Seems, there is some task on your server scheduled to run at 12:00 PM. Or there are network users of the server who start doing some heavy access at 12:00 PM.
The only maintenance FB does is "garbage collection" (geting rid of old record versions) and this is done on "when needed" basis (usually when records were selected, see the GCPolicy in firebird.conf) not on some predefined time.
Do you experience this hang only on during these certain hours or is it always slow to insert to that table? Have you checked the server load during the slowdown (ie in the task manager, is the CPU maxed out)? Anyway, here is some ideas to check:
What constraints / triggers do you have on the table? If they involve some extensive checks (ie against the other tables which contain millions of rows) this could be the reason inserts take so long.
Perhaps there is some other service which is triggered at that time? Ie do you have a cron job to make backup of the DB at that time? Or perhaps some other system service which runs at that time with higher priority slows down the server?
Do you have trace service active for the table? See fbtrace.conf in FireBird root directory. If it is active, extensive logging might be the cause of slowdown, if it isn't active, using it might help you to find the cause.
What are the setings for ForcedWrites / UnflushedWrites (see firebird.conf)? Does changing them make difference?
Is there something logged for this troublesome timeframe in firebird.log?
To me it looks like you have a process which starts at 12:00 and does something which locks the entire table. Use the monitoring table or the trace manager to see if there is any connection or active transaction which looks suspicious.
I also think your own transaction are started with the WAIT clause without a LOCK TIMEOUT, you might want to change this to NO WAIT or WAIT with a LOCK TIMEOUT, so that your transactions either fail immediately or after the timeout.
My suggestion is to use the TRACE API in 2.5 to track down what is happening near or around that time. That should help get you more information as to what is happening.
I use this for debugging http://upscene.com/products.misc.fbtm.php kinda buggy itself, but when it is working it is a god send.
Are some Client-Connections going DOWN at 12:00 PM? I had a similar problem on a 70.000 records sized table:
Client "A" has a permanently open DB Connection like "select * from TABLE". This is a "read only transaction" but reason enough for the server to generate Record-Versions. Why?
Client "B" made massive Updates to this Table, the Server tries to preserve the world like it was when "A" startet her "select". This is normal for Transaction able DB-Servers, and its implemented by creating Record Copies of the record-data before its updated.
So in my case for this TABLE 170.000 Record Versions existed. You can measure this by
gstat -r -t TABLE db.fdb | grep versions
If Client "B" goes down, the count of Record-Versions is NOT growing any more. Client "A" is the guilty one, freezing all this versions, forces the server to hold it. Finally if Client "A" goes down (or for example a firewall rule cuts all pending connections) Firebird is happy to start the process of getting rid of the now useless Record-Versions.
This "sweep"?! is bad programmed (even 2.5.2) cpu is 3% it do only <10.000 Versions / Minute so this TABLE has a performance of about 2%.
Ok so for standard, non-mirrored databases, the transaction log is kept in check either simply by having the database in simple mode or by doing regular backups. We keep ours in simple as we have SAN snapshot backups taking place and there is no need for SQL backups.
We're now going to mirroring. I obviously no longer have the choice of simple mode and must use full. this obviously leads to large log files and the need for log backups. That's fine I can deal with that; a maintenance plan that takes a log backup and discards any previous ones. I realise that this backup is essentially useless without its predecessors but the SAN snapshots are doing the backups.
My question is...
a) Is there a way to truncate the log file of all processed rows without creating a backup? (as I can't use them anyway...)
b) A maintenance plan is local to a server and is not replicated across a mirrored pair. How should it be done on a mirrored setup? such that when the database fails over, the plan starts running on the new principal, but doesn't get upset when its a mirror?
Thanks
A. If your server is important enough to mirror it, why isn't it important enough to take transaction log backups? SAN snapshots are point-in-time images of just one point in time, but they don't give you the ability to stop at different points of time along the way. When your developers truncate a table, you want to replay all of the logs right up until that statement, and stop there. That's what transaction log backups are good for.
B. Set up a maintenance plan (or even better, T-SQL scripts like Ola Hallengren's at http://ola.hallengren.com) to back up all of the databases, but check the boxes to only back up the online ones. (Off the top of my head, not sure if that's an option in 2005 - might be 2008 only.) That way, you'll always get whatever ones happen to fail over.
Of course, keep in mind that you need to be careful with things like cleanup scripts and copying those backup files. If you have half of your t-log backups on one share and half on the other, it's tougher to restore.
a) no, you cannot truncate a log that is part of a mirrored database. backing the logs up is your best option. I have several databases that are setup with mirroring simply based on teh HA needs but DR is not required for various reasons. That seems to be your situation? I would really still recommend keeping the log backups for a period of time. No reason to kill a perfectly good recovery plan that is added by your HA strategy. :)
b) My own solutions for this are to have a secondary agent job that monitors based on the status of the mirror. If the mirror is found to change, the secondary job on teh mirror instance is enabled and if possible, the old principal is disabled. if the principal was down and it comes back up, the job is still disabled. the only way the jobs themselves would be switched back is the event of again, another forced failover.
I have a myISAM table running in production on mySQL, and by doing a few tests, we've found we can tremendously speed up a query by adding a certain compound index. So far so good. However, I am not really about the best way to add this index in a production environment without locking the table for a long time (it's got 27GBs of data, so not so much, but it does take a while).
Do you have any tips? If this was a more sophisticated setup of course we'd have a live replica of all of the data on another machine, and we could safely switch. Unfortunately, we're not there yet, and I would like to speed up this query as soon as possible (it's causing big customer headaches). Is there some simple way to replicate the data and then do a swap-out trick? Some other tricks that I am missing?
UPDATE: Reading about "Online Index Operations" in SQL Server makes me very jealous http://msdn.microsoft.com/en-us/library/ms191261.aspx :)
Thanks!
you can use replication to get downtime on the order of a couple minutes, instead of the hours it might take to create an index on that table.
to set up the slave, see http://dev.mysql.com/doc/refman/5.0/en/replication-howto-existingdata.html
a recommendation i can make to help speed up the process is in step 2 follow the "Creating a Data Snapshot Using Raw Data Files" method. but instead of copying over the wire to the slave, copy to a different location on the master. and bring the master back up as soon at the copy is done and you've made the necessary changes to the config file (set server-id and enabled binary logging). this will minimize your downtime to just a minute or two. once the server is back up, you can copy the copied files to the slave box.
once you have the slave up and running and you have verified everything is replicating properly, you can pause the slave. create the index on the salve. when the index creation is complete, resume the slave. this will catch the slave up to the master. on the master, use FLUSH TABLE WITH READ LOCK. check the slave status to make sure the log position on the master and the slave match. if they do, shut down the slave and copy the files for that table back to the master.
I'm with Randy. We've been in a similar situation, and there are two ways in MySQL to accomplish something like this:
Take down the server while it runs. This is what you'll probably do. It's simple, it's easy, it works. Time to do? Maybe a half hour/45 minutes, dependent on disk bandwidth. See below.
Make a new table with the new index, copy all the data over, pause the server delete the first table, alter the new one to the old name, start the server. Downtime? 10 minutes, maybe, but really complicated.
Option two works, and saves you the downtime of creating the index (if it takes a long time). But it takes more space, it's more complicated (since you have to deal with the new records inserted off the main table, and it will probably lock on MyISAM while copying the data out. Deleting a table will take some time, altering the table to the new name will take some time. It's just really complicated. If you had a 2TB table this might be useful, but for 27G it's probably overkill.
Do you have a second server that is close in specifications to your production server? Load up your most recent backup and do the index there, so you know about how long it will take to add. Then plan for downtime.
InnoDB is better about many things, but new indexes still lock the table. Those abilities that MSSQL (and I think PostgreSQL) have to do those kind of things without locking would be great.
Find your low usage window and take your application offline during the index build. Since you don't have replication or a multimaster or whatever, you're just going to have to bite the bullet on this one. See you at 1am. :-)
Not much you can do with one server here.
If you copy the table and do a dry run, at least you'll find out how long it's going to take without locking the live table, so you can schedule some maintenance time if necessary, or make a decision whether you can just push the button and leave users hanging for a couple of minutes :)
Or schedule it for a quiet time...
at 04:00 /usr/bin/mysql -uXXX -pXXX -e 'alter table mytable add key(col1, col2)'
We are using Replication and seem to be having endless problems with it. It seems to shut down for unknown reasons. It needs to be shut down to remove a column and only starts back up half the time. Does anyone have any advice on how to properly use replication or some alternatives to it.
Edit:
We are using Sql Server 2005, We cannot use database mirroring as we used the other database for reporting. As far as I am aware you cannot query from a mirrored database.
If you need just couple of tables from your DB for reports, replication is more useful, but you also can set up log shipping with secondary server in STAND BY mode (especially if you need significant part of your data for reports), then you can run reports on secondary server. You just have to remember that log shipping will interfere with transaction log backups, so you have to use the same folder with log backup files for both processes.
I would think the combination of database mirroring and database snapshots will solve your issues.
First, database mirroring is very easy to setup and I have never had any problems with it (using it for the past 4+ years).
Second, creating a database snapshot on your failover server will allow you to run reports. You can setup a sql agent job to drop and re-create the snapshot on whatever acceptable interval you like.
Of course this is all dependent on if you need your reports to run on real-time data or if they can be delayed somewhat.
Here are a list of the problems that I have had to resolve to get replication working:
1) The replication sometimes lies to me and tells me this, even when its working fine.
"The server 'Bob' is not a Subscriber. (.Net SqlClient Data Provider)" I have tried to re-initialise it thinking that it was broken and it never was...
2) It can take a little while to restart itself, especially if your remote DB is on the other side of the planet, which it is in my case. If you are on a slow network connection, or it is not 100% reliable, then you can have problems. Also, the jobs which restart the process can sometimes take a while to run, which also delays things further.
3) Some changes require full re-initalisation which involves sending a new snapshot out. If you don't have your permissions quite right, and you can re-initialise manually, but it doesn't happen automatically, then this can be a another reason for problems.
We have a SQL transactional replication which runs perfectly happily. You seem to say that it is when you are making schema changes to the publisher that you get problems. Each time we do a schema change we drop the publication, subscription and the subscription database. Do the change, then re-build it all. We can do this becuase we can tolerate the time it takes to re-apply the snapshot. There are ways to apply schema changes to the publication and have them propogate to the subscriber. Take a look at sp_register_custom_scripting. We have made this work once, so I can give some more information about it if you need.
As #Jason says, you can report from a mirrored database by using a snapshot. Beware that the snapshot will take up space, and cause more work for the mirror server. Although how much space will depend on how much data is changing and how big your original database is. We do use a snapshot on a mirrored database for occasional reports because our entire database is not replicated.
log shipping http://msdn.microsoft.com/en-us/library/ms187103.aspx
What version of SQL Server are you using?
We're using replication now for a particular solution, and it seems to just work, day in, day out.
I would examine your event log's, and SQL Server logs to see if you can determine why it is shutting down, and why it doesn't start up.
Are you possibly patching the servers, or are you having network errors?
The alternatives to replication are log shipping, or database mirroring.
I personally prefer Database Mirroring, but it really depends what you're trying to do, as some of these aren't appropriate for certain situations.
We also have used SQL transactional replication. We had the same pains with updating schema, which requires dropping the publication on all servers, performing the updates, and then reinitializing replication, and hoping for the best. Sometimes it would not initialize, or a node would fall behind and we'd get little warning for it. A few times we even lost all the stored procedure execute permissions causing pretty much total failure on the websites.
We have a rather large database so reinitialization could take quite some time, meaning all updates had to be done at 2am on Sunday - not exactly when we're awake and alert and able to use all our faculties to deal with a problem that might arise.
We are ditching replication in favor of failover clustering on SQL 2008, but it can still be done all the way back to SQL 2000.
http://technet.microsoft.com/en-us/library/cc917693.aspx