How long doe it take to add a new node? I'm 100% sure neither 90s nor
120s is the answer. The answer is it varies. If you want to wait for
finishing adding a new node, be explicit about it, wait for the node
fully joins the cluster. Don't put a fixed number of seconds in there.
You can estimate the time for adding many nodes once you've had added a
node to the cluster. The time not only depends on the data size,
hardware and network, but also the data in the SSTables files. For
example, if a full copy of a very large partition exists in may SSTables
files but the latest one of them is a tombstone, then the actual data
get streamed is only the tombstone, not the other copies of large data.
BTW, for your own sake, you should consider automate the process to
minimise human interactions required to add multiple nodes. It may be
manageable when you have 5 or 10 nodes to add, but it will quickly spin
off control when you have tons or a few hundred of them.
On 11/07/2022 10:41, Marc Hoppins wrote:
“Where did you come up with the 90 seconds number?” The database folk
came up with THAT number. For myself, I timed adding a new node at 120
seconds for the initial setup with no data in the cluster.
“What exactly are you waiting for by doing that?” I wanted to see for
myself how long it took to add a new node. Isn’t that what RESEARCH
is all about? I suppose I could have just ‘googled’ it.
“Since adding nodes doesn't interfere with the client queries, the
time it takes to add a node shouldn't be a concern at all…” It IS a
concern if one has to add many nodes and the ‘customers’ want some
idea of how long the process will take. Or, and I may be alone in
this, it would be helpful to know when to begin adding the next new
node in the ticket. Therefore, if I know when my first node is
finished, I will have an idea of how long before I check for the when
subsequent nodes can be joined.
*From:*Bowen Song via user <user@cassandra.apache.org>
*Sent:* Monday, July 11, 2022 11:25 AM
*To:* user@cassandra.apache.org
*Subject:* Re: Adding nodes
EXTERNAL
Sleeping/pausing for a fixed amount of time between operations at best
is a hack to workaround an unknown issue, but it's almost always
better to be explicit about what you are waiting for. Where did you
come up with the 90 seconds number? What exactly are you waiting for
by doing that? If you want to wait for the node's state becomes normal
(from joining), be explicit about it, check the nodetool output or the
system.log file periodically instead of waiting for a fixed 90 seconds.
Streaming 600GB in a few hours sounds fairly reasonable. Since adding
nodes doesn't interfere with the client queries, the time it takes to
add a node shouldn't be a concern at all, as long as it's
significantly faster the data growth rate. Just leave it running in
the background, and get on with your life.
If you must speed up that process and don't care about data
inconstancy or potencial down time, there's faster ways to do it, but
doing that breaks the consistency and/or availability, which means it
will interfere with client read/write operations.
A few hundred GB to a few TB per node is pretty common in Cassandra
clusters. Big data is not about how much data on EACH node, it's about
how much data in TOTAL.
On 11/07/2022 09:01, Marc Hoppins wrote:
Well then…
I left this on Friday (still running) and came back to it today
(Monday) to find the service stopped. So, I blitzed this node
from the ring and began anew with a different new node.
I rather suspect the problem was with trying to use Ansible to add
these initially - despite the fact that I had a serial limit of 1
and a pause of 90s for starting the service on each new node
(based on the time taken when setting up this Cassandra cluster).
So…moving forward…
It is recommended to only add one new node at a time from what I
read. This leads me to:
Although I see the new node LOAD is progressing far faster than
the previous failure, it is still going to take several hours to
move from UJ to UN, which means I’ll be at this all week for the
12 new nodes. If our LOAD per node is around 400-600GB, is there
any practical method to speed up adding multiple new nodes which
is unlikely to cause problems? After all, in the modern world of
big (how big is big?) data, 600G per node is far less than the
real BIG big-data.
Marc
*From:*Jeff Jirsa <jji...@gmail.com> <mailto:jji...@gmail.com>
*Sent:* Friday, July 8, 2022 5:46 PM
*To:* cassandra <user@cassandra.apache.org>
<mailto:user@cassandra.apache.org>
*Cc:* Bowen Song <bo...@bso.ng> <mailto:bo...@bso.ng>
*Subject:* Re: Adding nodes
EXTERNAL
Having a node UJ but not sending/receiving other streams is an
invalid state (unless 4.0 moved the streaming data out of
netstats? I'm not 100% sure, but I'm 99% sure it should be there).
It likely stopped the bootstrap process long ago with an error
(which you may not have seen), and is running without being in the
ring, but also not trying to join the ring.
145GB vs 1.1T could be bits vs bytes (that's a factor of 8), or it
could be that you streamed data and compacted it away. Hard to
say, but less important - the fact that it's UJ but not streaming
means there's a different problem.
If it's me, I do this (not guaranteed to work, your mileage may
vary, etc):
1) Look for errors in the logs of ALL hosts. In the joining host,
look for an exception that stops bootstrap. In the others, look
for messages about errors streaming, and/or exceptions around file
access. In all of those hosts, check to see if any of them think
they're streaming ( nodetool netstats again)
2) Stop the joining host. It's almost certainly not going to
finish now. Remove data directories, commitlog directory, saved
caches, hints. Wait 2 minutes. Make sure every other host in the
cluster sees it disappear from the ring. Then, start it fresh and
let it bootstrap again. (you could alternatively try the resumable
bootstrap option, but I never use it).
On Fri, Jul 8, 2022 at 2:56 AM Marc Hoppins
<marc.hopp...@eset.com> wrote:
Ifconfig shows RX of 1.1T. This doesn't seem to fit with the
LOAD of 145GiB (nodetool status), unless I am reading that
wrong...and the fact that this node still has a status of UJ.
Netstats on this node shows (other than :
Read Repair Statistics:
Attempted: 0
Mismatch (Blocking): 0
Mismatch (Background): 0
Pool Name Active Pending Completed Dropped
Large messages n/a 0 0 0
Small messages n/a 53 569755545 15740262
Gossip messages n/a 0 288878 2
None of this addresses the issue of not being able to add more
nodes.
-----Original Message-----
From: Bowen Song via user <user@cassandra.apache.org>
Sent: Friday, July 8, 2022 11:47 AM
To: user@cassandra.apache.org
Subject: Re: Adding nodes
EXTERNAL
I would assume that's 85 GB (i.e. gigabytes) then. Which is
approximately 79 GiB (i.e. gibibytes). This still sounds
awfully slow - less than 1MB/s over a full day (24 hours).
You said CPU and network aren't the bottleneck. Have you
checked the disk IO? Also, be mindful with CPU usage. It can
still be a bottleneck if one thread uses 100% of a CPU core
while all other cores are idle.
On 08/07/2022 07:09, Marc Hoppins wrote:
> Thank you for pointing that out.
>
> 85 gigabytes/gibibytes/GIGABYTES/GIBIBYTES/whatever name you
care to
> give it
>
> CPU and bandwidth are not the problem.
>
> Version 4.0.3 but, as I stated, all nodes use the same
version so the version is not important either.
>
> Existing nodes have 350-400+(choose whatever you want to call a
> gigabyte)
>
> The problem appears to be that adding new nodes is a serial
process, which is fine when there is no data and each node is
added within 2minutes. It is hardly practical in production.
>
> -----Original Message-----
> From: Bowen Song via user <user@cassandra.apache.org>
> Sent: Thursday, July 7, 2022 8:43 PM
> To: user@cassandra.apache.org
> Subject: Re: Adding nodes
>
> EXTERNAL
>
>
> 86Gb (that's gigabits, which is 10.75GB, gigabytes) took an
entire day seems obviously too long. I would check the network
bandwidth, disk IO and CPU usage and find out what is the
bottleneck.
>
> On 07/07/2022 15:48, Marc Hoppins wrote:
>> Hi all,
>>
>> Cluster of 2 DC and 24 nodes
>>
>> DC1 (RF3) = 12 nodes, 16 tokens each
>> DC2 (RF3) = 12 nodes, 16 tokens each
>>
>> Adding 12 more nodes to DC1: I installed Cassandra (version
is the same across all nodes) but, after the first node added,
I couldn't seem to add any further nodes.
>>
>> I check nodetool status and the newly added node is UJ. It
remains this way all day and only 86Gb of data is added to the
node over the entire day (probably not yet complete). This
seems a little slow and, more than a little inconvenient to
only be able to add one node at a time - or at least one node
every 2 minutes. When the cluster was created, I timed each
node from service start to status UJ (having a UUID) and it
was around 120 seconds. Of course there was no data.
>>
>> Is it possible I have some setting not correctly tuned?
>>
>> Thanks
>>
>> Marc
