Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
I'm wondering if the new kernel option "drop_caches" would allow read
only access to the secondary?
http://linux.inet.hr/proc_sys_vm_drop_caches.html
The reason I want this is for the following scenario
* Primary machine has a small DRDB partition with the Postgres "write
ahead log" (perhaps stored in a battery backed RAM disk for performance)
* Secondary machine has a copy of the PG database, and, as long as it
can READ the write ahead log mirror (DRBD or Raid1), it can keep a hot
remote ACID compliant backup of the postgres database.
Something like this on the secondary
while true
do
mount -o ro /mnt/pg_wal
process new WAL entries (this is a read only op, on what is basically
a sequential file that just gets added to by the primary)
umount /mnt/pg_wal
echo 3 > /proc/sys/vm/drop_caches # see below
sleep 2
done
Here's the details from the above link, about the new proc option. Can
anyone give me any feedback on whether this is a viable option?
------------------------
drop_caches
Writing to this will cause the kernel to drop clean caches, dentries and
inodes from memory, causing that memory to become free.
To free pagecache:
* echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
* echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
* echo 3 > /proc/sys/vm/drop_caches
As this is a non-destructive operation and dirty objects are not
freeable, the user should run "sync" first.
Dr. Volker Jaenisch wrote:
> Hi DRBD People!
>
> drbd0.7 is in production on some of our customers sites.
> Thank you very much for this fine pice of software.
>
> Now we are curious on DRBD8.
> We have a testing instance of drbd8-pre3 running smootly on two debian
> etch servers ACTIVE/PASSIVE.
> Is there any documentation to setup ACTIVE/ACTIVE yet?
> Please give us some hints to satisfy our curiousity.
>
> Best Regards
>
> Volker
>