Syncer Daemon

[Thomas Lee_1]

I know that there are /sbin/init.d/syncer
which call for "syncer".

Now I would like to what's the meaning for option syncer -d /mount/point? As I'm not
native english speaker, I dun understand the
exact meaning in man about syncer.

I looking for syncer becos, I have using dbc_max_pct/dbc_min_pct for a Oracle Server. But I dun have Advanced JFS, so can't use option in mount like 'mincache=direct', and would like to know if syncer -d can solve my problem or it got another usage.

Or there any other option for me to let some mount point using cache but some other not using cache.

TIA~!

[T G Manikandan · Accepted solution]

syncer is used to sync the data from the memory to the hard disk at frequent intervals to prevent huge data loss in case of a system crash.

This program is run frequently default 30 secs.

-d option is used to place directories in the cache.
If there are some directories which are frequently accessed placing these large directories in the cache would increase performance.

Thanks

[Michael Tully]

There is a man page for this command. The syncer command flushes information from cache to the actual disk. You do no need to run this command directly, as it runs in the background. You can change the options if required ,to do so. The changes would need to made in /sbin/init.d/syncer even though it suggests not to by changing the default setting of 30 seconds to a lower value. I've not done this so I don't what the actual consequences of doing it will be.

[Thomas Lee_1]

Manikandan
So what's the arrange if by default there are not -d option submit?
Or if I use -d option, isn't that other mount point will have no cache?

[T G Manikandan]

It is like those directories will be open or placed in cache when a process requires.
the -d option tells like place/open this dir on the cache as this dir is a frequently accessed dir.

[Mark Grant]

Thomas,If you don't have -d, syncer will not cache anything. If you use "-d" and then a directory name, it will cache that.

[Con O'Kelly]

Hi Thomas

There isn't a way to bypass buffer cache for Oracle filesystems without having OnlineJFS unless of course you use raw devices.

You will find alot of discussions about these Online JFS options for Oracle on the forums & it appears that performance can improve a little bit but only in a small number of cases.

I'd pay more attention to correctly sizing your SGA and ensuring there is efficient SQL code etc.

For your buffer cache look at a size of around 300-400MB for 11.x and a bit more for 11i.

Cheers
Con

[Thomas Lee_1]

Mark Grant

So you mean that even I have a 300M dynamic buffer cache, it will cache nothing if I haven't use -d?

[Con O'Kelly]

Hi Thomas

No that's not correct. You don't need to use -d for syncer daemon, caching will still work fine.
A Buffer cache of 300MB sounds fine.

Cheers
Con

[Mark Grant]

Thomas, the syncer -d option is not related to buffer cache. It is for the syncer to cache stuff just to make the syncer work a bit quicker in some instances. It really is not the tool you need here, I'm pretty sure about that!Regards