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Date: Thu, 31 Jan 2013 10:50:40 -0800 (PST)
From: Wei Zhu <wz1975@yahoo.com>
Reply-To: Wei Zhu <wz1975@yahoo.com>
Subject: General question regarding bootstrap and nodetool repair
To: Cassandr usergroup <user@cassandra.apache.org>
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Hi,=0AAfter messing around with my Cassandra cluster recently, I think I ne=
ed some basic understanding on how things work behind scene regarding data =
streaming.=0ALet's say we have three node cluster with RF =3D 3. =A0If node=
 3 for some reason dies and I want to replace it with a new node with the s=
ame (maybe minus one) range. During the bootstrap, how the data is streamed=
?=0AFrom what I observed, Node 3 has replicates for its primary range on no=
de 4, 5. So it streams the data from them and starts to compact them. Also,=
 node 3 holds replicates for primary range of node 2, so it streams data fr=
om node 2 and node 4. Similarly, it holds replicates for node 1. So data st=
reamed from node 1 and node 2. So during the bootstaping, it basically gets=
 the data from all the replicates (2 copies each), so it will require doubl=
e the disk space in order to hold the data? Over the time, those SStables w=
ill be compacted and redundant will be removed? Is it true?=0A=0Aif we issu=
e nodetool repair -pr on node 3, apart from streaming data from node 4, 5 t=
o 3. We also see data stream between node 4, 5 since they hold the replicat=
es. But I don't see log regarding "merkle tree calculation" on node 4,5. Ju=
st wondering how they know what data to stream in order to repair node 4, 5=
?=0A=0AThanks.=0A-Wei=0A
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<html><body><div style=3D"color:#000; background-color:#fff; font-family:ar=
ial, helvetica, sans-serif;font-size:10pt"><div style=3D"font-family: arial=
, helvetica, sans-serif; font-size: 10pt; ">Hi,</div><div style=3D"font-fam=
ily: arial, helvetica, sans-serif; font-size: 10pt; ">After messing around =
with my Cassandra cluster recently, I think I need some basic understanding=
 on how things work behind scene regarding data streaming.</div><div style=
=3D"font-family: arial, helvetica, sans-serif; font-size: 10pt; ">Let's say=
 we have three node cluster with RF =3D 3. &nbsp;If node 3 for some reason =
dies and I want to replace it with a new node with the same (maybe minus on=
e) range. During the bootstrap, how the data is streamed?</div><div style=
=3D"font-family: arial, helvetica, sans-serif; font-size: 10pt; ">From what=
 I observed, Node 3 has replicates for its primary range on node 4, 5. So i=
t streams the data from them and starts to compact them. Also, node 3 holds
 replicates for primary range of node 2, so it streams data from node 2 and=
 node 4. Similarly, it holds replicates for node 1. So data streamed from n=
ode 1 and node 2. So during the bootstaping, it basically gets the data fro=
m all the replicates (2 copies each), so it will require double the disk sp=
ace in order to hold the data? Over the time, those SStables will be compac=
ted and redundant will be removed? Is it true?</div><div style=3D"font-fami=
ly: arial, helvetica, sans-serif; font-size: 10pt; "><br></div><div style=
=3D"font-family: arial, helvetica, sans-serif; font-size: 13px; color: rgb(=
0, 0, 0); background-color: transparent; font-style: normal; ">if we issue =
nodetool repair -pr on node 3, apart from streaming data from node 4, 5 to =
3. We also see data stream between node 4, 5 since they hold the replicates=
. But I don't see log regarding "merkle tree calculation" on node 4,5. Just=
 wondering how they know what data to stream in order to repair node 4,
 5?</div><div style=3D"font-family: arial, helvetica, sans-serif; font-size=
: 13px; color: rgb(0, 0, 0); background-color: transparent; font-style: nor=
mal; "><br></div><div style=3D"font-family: arial, helvetica, sans-serif; f=
ont-size: 13px; color: rgb(0, 0, 0); background-color: transparent; font-st=
yle: normal; ">Thanks.</div><div style=3D"font-family: arial, helvetica, sa=
ns-serif; font-size: 13px; color: rgb(0, 0, 0); background-color: transpare=
nt; font-style: normal; ">-Wei</div><div style=3D"font-family: arial, helve=
tica, sans-serif; font-size: 10pt; "><br></div></div></body></html>
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