The reason I asked about nsslapd-threadnumber is because during the time of
the spike, all transactions slow. Meaning that binds, adds, searches, ect.
all start increasing in their etime until it hits the point where we've
processed the majority of writes and then etimes fall back to 0.The
customer in this case is doing 1k Adds to a subtree, an object with 10
attributes, three of which are indexed. I will also try the micro second
logging in test and see if I can recreate the issue and maybe see something
there. Hopefully that explanation gives you a little more insight into our
issue. I really don't want to affect other customers by this bad one.
"Replication on the supplier side or replication on the consumer side."
The consumer takes the burst of writes into it's on database fine through
replication, but they're coming in obviously on a single replication
session. It's using the same hardware/ds version.
FWIW we're using 1.2.11 on RHEL5.4, we're switching over to 1.3.1 on RHEL6
in a few months.
On Wed, Aug 21, 2013 at 7:09 AM, Rich Megginson <rmeggins(a)redhat.com> wrote:
On 08/20/2013 08:39 PM, Jeffrey Dunham wrote:
We have a customer that has been multi-threading behind multiple
servers and writing to our Master server. These writes come in the form
of heavy spikes (1k over 5 second intervals) very much burst traffic and
all the writes are adding new items to the same ou.
What is the platform? What version of 389-ds-base? How much RAM do you
have? What is the size of your database?
While we have plans to throttle them I had a few questions:
a) If they're writing to the same ou / updating the same indexes are they
blocked on one items success before another succeeds?
Yes.
So in this case multi threading behind multiple boxes does not give
them any performance impact. I would guess this is the case, but I want to
be sure. Because replication seems to be fine which goes through a single
thread iirc.
Replication on the supplier side or replication on the consumer side.
b) are there any performance tweaks that can help? I thought maybe
looking at nsslapd-threadnumber.
To speed up writes? That might help, but not much, since your bottleneck
is that only one write can happen at a time.
The first thing you should do is optimize your db and entry cache usage.
You can use the
https://github.com/richm/scripts/wiki/dbmon.sh script to
monitor your cache usage, and find out how much RAM you need for your
caches, and find out how much RAM you have left over for other tuning.
1) Try putting the db home directory on a RAM disk. By default, bdb uses
memory mapped files in /var/lib/dirsrv/slapd-INST/db. These have to be
flushed to disk. Change nsslapd-db-home-directory to point to a RAM fs.
mkdir /dev/shm/slapd-INST ; chown nobody:nobody /dev/shm/slapd-INST ;
chmod 0600 /dev/shm/slapd-INST
Then shutdown dirsrv, edit /etc/dirsrv/slapd-INST/dse.ldif
in the dn: cn=config,cn=ldbm database,cn=plugins,cn=config entry, add
nsslapd-db-home-directory: /dev/shm/slapd-INST
NOTE: This will use the amount of RAM specified by nsslapd-dbcachesize, so
make sure you have enough RAM.
https://access.redhat.com/site/documentation/en-US/Red_Hat_Directory_Serv...
2) Use different physical disks for your db directory, transaction log
directory, and server log directory. If you can afford it, use a disk
controller with a write back cache for the disk used for the transaction
logs.
3) If you can afford the possibility of data loss, you can disable durable
transactions.
-Jeff
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