Thanks, that one worked :-)
On Sep 22, 2015, at 3:28 PM, James Heather
<[email protected]<mailto:[email protected]>> wrote:
Try the one you missed:
SYSTEM."SEQUENCE"
i.e., quote the bits separately (but SYSTEM doesn't need quoting), and put it
in caps.
James
On 22/09/15 21:18, Michael McAllister wrote:
More failed attempts ...
0: jdbc:phoenix:redacted,> select count(*) from system."sequence";
Error: ERROR 1012 (42M03): Table undefined. tableName=SYSTEM.sequence
(state=42M03,code=1012)
0: jdbc:phoenix:redacted,> select count(*) from "system.sequence";
Error: ERROR 1012 (42M03): Table undefined. tableName=system.sequence
(state=42M03,code=1012)
0: jdbc:phoenix:redacted,> select count(*) from "SYSTEM.SEQUENCE";
Error: ERROR 1012 (42M03): Table undefined. tableName=SYSTEM.SEQUENCE
(state=42M03,code=1012)
Michael McAllister
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On Sep 22, 2015, at 3:14 PM, James Heather
<[email protected]<mailto:[email protected]>> wrote:
I don't think it's trying to stop you looking inside the table. I think it's
complaining that SEQUENCE is a keyword, and shouldn't be appearing there.
You could try quoting it.
James
On 22/09/15 21:11, Michael McAllister wrote:
OK - so the traditional methods of recreating sequences, that makes sense.
Interestingly btw, at least from within Phoenix I can’t see the content of
SYSTEM.SEQUENCE. I get the following error:-
0: jdbc:phoenix:redacted,> select count(*) from system.sequence;
Error: ERROR 604 (42P00): Syntax error. Mismatched input. Expecting "NAME", got
"sequence" at line 1, column 29. (state=42P00,code=604)
I do understand this is a system table, but it would be nice to see inside it.
This is from Apache Phoenix 4.2 on HDP 2.2.6.
Michael McAllister
Staff Data Warehouse Engineer | Decision Systems
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On Sep 22, 2015, at 2:47 PM, James Heather
<[email protected]<mailto:[email protected]>> wrote:
If no one else will be hitting the table while you complete the operation, and
if you don't mind about missing a few sequence values (i.e., having a gap), you
should just need the following.
SELECT NEXT VALUE FOR sequencename FROM sometable;
That will tell you the next value the sequence wants to hand out.
DROP SEQUENCE sequencename;
Then reconnect with the property as given below, and
CREATE SEQUENCE sequencename START WITH n;
where n is the value you retrieved in the first step.
The reason this might cause gaps is that client connections will cache sequence
values, so the one you retrieve might not actually be the first one that hasn't
been used; it'll just be the first one cached by the connection you're using.
But if you do it this way, and nothing else is connected in the meantime, then
you won't get any duplicates.
As far as I can see, if you're the only connected client, this should do it
with no gaps: no other clients will have cached any sequence values, so you'll
retrieve the first one your connection has cached (which will be the first one
available), and then that's where your sequence will start when you recreate
the sequence. But I'm not absolutely certain about that, and you might want to
try some experiments.
If the sequence is being used for a primary key column (a sort of
auto_increment), then the other option is to
SELECT MAX(id) FROM sometable;
and then add one to this value to determine where the recreated sequence should
start. That will ensure no gaps.
James
On 22/09/15 19:47, Michael McAllister wrote:
Mujtaba
Thanks for this information. Seeing as I am using Phoenix 4.2, what is the safe
and approved sequence of steps to drop this table and recreate it as you
mention? Additionally, how do we ensure we don’t lose sequence data?
Michael McAllister
Staff Data Warehouse Engineer | Decision Systems
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On Sep 22, 2015, at 1:32 PM, Mujtaba Chohan
<<mailto:[email protected]>[email protected]<mailto:[email protected]>>
wrote:
Since Phoenix 4.5.x default has been changed for phoenix.sequence.saltBuckets
to not split sequence table. See
this<https://git-wip-us.apache.org/repos/asf?p=phoenix.git;a=blobdiff;f=phoenix-core/src/main/java/org/apache/phoenix/query/QueryServicesOptions.java;h=79776e7f688fc700275d0502e31646afe2bbcb1e;hp=4e8879b1b7a6358db2c1f9ccb4fa169394fec721;hb=18e52cc4ce2384bdc7a9c72d63901058e40f04ae;hpb=b82c5cbccdf4eb944238e69a514841be361bfb6d>
commit. For older versions you can drop sequence table and reconnect with
setting client side phoenix.sequence.saltBuckets property.
On Tue, Sep 22, 2015 at 11:14 AM, Michael McAllister
<<mailto:[email protected]>[email protected]<mailto:[email protected]>>
wrote:
Hi
By default SYSTEM.SEQUENCE is installed with 256 regions. In an environment
where you don’t have a large number of tables and regions (yet), the end result
of this seems to be that with hbase balance_switch=true, you end up with a lot
of region servers with nothing but empty SYSTEM.SEQUENCE regions on them. That
mans inefficient use of our cluster.
Have there been any best practices developed as to how to deal with this
situation?
Michael McAllister
Staff Data Warehouse Engineer | Decision Systems
<mailto:[email protected]>[email protected]<mailto:[email protected]>
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michael.mcallister.ha<mailto:[email protected]> | webex:
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