Re: [GENERAL] Restart a sequence regularly
In article [EMAIL PROTECTED], Richard Huxton [EMAIL PROTECTED] writes: Kathy Lo wrote: On 11/21/07, Richard Huxton [EMAIL PROTECTED] wrote: You probably shouldn't attach any meaning to the numbers from a sequence - they're just guaranteed to be unique, nothing else. What you say here contradicts the following. Actually, the sequence is formed by 4-digit of year and 6-digit of sequence. So you *are* attaching significance to the number (by adding the current year to the front of it). Don't block users - have multiple sequences. If you define my_seq_2007, my_seq_2008, my_seq_2009 etc and then wrap access to them in a function you can EXTRACT() the year from the CURRENT_DATE and use that to form your per-year unique value. Since sequences don't guarantee consecutivity anyway, why not just use one sequence and prepend the year, e.g. by a view? ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [GENERAL] Restart a sequence regularly
Scott Marlowe wrote: revoke all privs on the sequence to anyone but the user about to reset it reset it grant the options back Quoting the OP: That means, when others want to access the sequence between 31-Dec 23:59:55 and 1-Jan 00:00:05, they are waiting instead of getting an error. If you remove the privs, clients will get an error, unless I'm missing something. .TM. -- / / / / / / Marco Colombo ___/ ___ / / Technical Manager / / / ESI s.r.l. _/ _/ _/ [EMAIL PROTECTED] ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org/
Re: [GENERAL] Restart a sequence regularly
Kathy Lo wrote:
Hi,
I am using Postgresql 8.0.3 in Fedora Core 4.
In my database, it contains a sequence. And, I need to alter the range
of this sequence and restart it to the start of the new range at
00:00:00 on 1st January on every year. 5 seconds before and after that
time, I need to prevent users from calling nextval() to retrieve the
next number from this sequence.
You probably shouldn't attach any meaning to the numbers from a sequence
- they're just guaranteed to be unique, nothing else.
I can write a Perl script to alter the sequence and schedule to run
this script at 23:59:55 on 31st December on every year.
But, I don't know how to lock the sequence to prevent others from
accessing this sequence to get next number and Postgresql does not
support to lock a sequence.
That would defeat the point of a sequence.
How can I prevent others from accessing the sequence, like locking a
table? That means, when others want to access the sequence between
31-Dec 23:59:55 and 1-Jan 00:00:05, they are waiting instead of
getting an error.
If you just want a new range of numbers to start 1st Jan, you could wrap
nextval() in another function that adds a base-value in depending on the
current date. Something like:
SELECT EXTRACT('YEAR' FROM CURRENT_DATE)*1000 + nextval(...)
If you really need to lock the sequence again, wrap it in another
function and have that function sleep for the required changeover period.
Of the top of my head it sounds awkward though - can you explain more
about how you're using this?
--
Richard Huxton
Archonet Ltd
---(end of broadcast)---
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
Re: [GENERAL] Restart a sequence regularly
On Nov 21, 2007 1:39 AM, Kathy Lo [EMAIL PROTECTED] wrote: Hi, I am using Postgresql 8.0.3 in Fedora Core 4. In my database, it contains a sequence. And, I need to alter the range of this sequence and restart it to the start of the new range at 00:00:00 on 1st January on every year. 5 seconds before and after that time, I need to prevent users from calling nextval() to retrieve the next number from this sequence. I can write a Perl script to alter the sequence and schedule to run this script at 23:59:55 on 31st December on every year. revoke all privs on the sequence to anyone but the user about to reset it reset it grant the options back ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [GENERAL] Restart a sequence regularly
On Nov 21, 2007 11:44 AM, Marco Colombo [EMAIL PROTECTED] wrote: Scott Marlowe wrote: revoke all privs on the sequence to anyone but the user about to reset it reset it grant the options back Quoting the OP: That means, when others want to access the sequence between 31-Dec 23:59:55 and 1-Jan 00:00:05, they are waiting instead of getting an error. If you remove the privs, clients will get an error, unless I'm missing something. Good point. I'm guessing if you need a way to make other users wait, not get an error, you'll need to use a funtion with a security definer that will sleep or something during that period. hm. ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [GENERAL] Restart a sequence regularly
Scott Marlowe [EMAIL PROTECTED] writes:
Good point. I'm guessing if you need a way to make other users wait,
not get an error, you'll need to use a funtion with a security definer
that will sleep or something during that period.
What you'd want is to take out an exclusive lock on the sequence.
[ fools around... ] Hmm, we don't let you do LOCK TABLE on a sequence,
which is perhaps overly restrictive, but you can get the same effect
with any ALTER TABLE command that works on a sequence. For instance
a no-op ALTER OWNER:
Session 1:
regression=# create sequence s;
CREATE SEQUENCE
regression=# begin;
BEGIN
regression=# alter table s owner to postgres;
ALTER TABLE
Session 2;
regression=# select nextval('s');
[ hangs ... ]
Session 1:
regression=# alter sequence s restart with 42;
ALTER SEQUENCE
regression=# commit;
COMMIT
Session 2:
nextval
-
42
(1 row)
regards, tom lane
---(end of broadcast)---
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
Re: [GENERAL] Restart a sequence regularly
On 11/21/07, Richard Huxton [EMAIL PROTECTED] wrote:
Kathy Lo wrote:
Hi,
I am using Postgresql 8.0.3 in Fedora Core 4.
In my database, it contains a sequence. And, I need to alter the range
of this sequence and restart it to the start of the new range at
00:00:00 on 1st January on every year. 5 seconds before and after that
time, I need to prevent users from calling nextval() to retrieve the
next number from this sequence.
You probably shouldn't attach any meaning to the numbers from a sequence
- they're just guaranteed to be unique, nothing else.
Yes, the sequence is just for guaranted that every users can get a
unique number. It does not relate to any tables
I can write a Perl script to alter the sequence and schedule to run
this script at 23:59:55 on 31st December on every year.
But, I don't know how to lock the sequence to prevent others from
accessing this sequence to get next number and Postgresql does not
support to lock a sequence.
That would defeat the point of a sequence.
How can I prevent others from accessing the sequence, like locking a
table? That means, when others want to access the sequence between
31-Dec 23:59:55 and 1-Jan 00:00:05, they are waiting instead of
getting an error.
If you just want a new range of numbers to start 1st Jan, you could wrap
nextval() in another function that adds a base-value in depending on the
current date. Something like:
SELECT EXTRACT('YEAR' FROM CURRENT_DATE)*1000 + nextval(...)
If you really need to lock the sequence again, wrap it in another
function and have that function sleep for the required changeover period.
Of the top of my head it sounds awkward though - can you explain more
about how you're using this?
Actually, the sequence is formed by 4-digit of year and 6-digit of
sequence. So, it is required to change and restart the range of
sequence at the beginning of every year. For example, at the beginning
of 2008, the sequence should be changed to the range of 200801 -
200899 and restart at 200801. In the time of changing the
sequence, it does not allow any users to get the unique number from
this sequence. However, our staff don't want to do it manually because
it is difficult for them to make sure no one accessing the sequence
and our service cannot stop at that time. Therefore, I need to let the
users to wait in the period of changing the sequence.
--
Richard Huxton
Archonet Ltd
--
Kathy Lo
---(end of broadcast)---
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
Re: [GENERAL] Restart a sequence regularly
On 11/22/07, Tom Lane [EMAIL PROTECTED] wrote:
Scott Marlowe [EMAIL PROTECTED] writes:
Good point. I'm guessing if you need a way to make other users wait,
not get an error, you'll need to use a funtion with a security definer
that will sleep or something during that period.
What you'd want is to take out an exclusive lock on the sequence.
[ fools around... ] Hmm, we don't let you do LOCK TABLE on a sequence,
which is perhaps overly restrictive, but you can get the same effect
with any ALTER TABLE command that works on a sequence. For instance
a no-op ALTER OWNER:
Session 1:
regression=# create sequence s;
CREATE SEQUENCE
regression=# begin;
BEGIN
regression=# alter table s owner to postgres;
ALTER TABLE
Session 2;
regression=# select nextval('s');
[ hangs ... ]
Session 1:
regression=# alter sequence s restart with 42;
ALTER SEQUENCE
regression=# commit;
COMMIT
Session 2:
nextval
-
42
(1 row)
regards, tom lane
---(end of broadcast)---
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
Thanks for your reply.
But, the owner of the sequence originally is postgres. Does it work?
--
Kathy Lo
---(end of broadcast)---
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
Re: [GENERAL] Restart a sequence regularly
On 11/22/07, Scott Marlowe [EMAIL PROTECTED] wrote: On Nov 21, 2007 11:44 AM, Marco Colombo [EMAIL PROTECTED] wrote: Scott Marlowe wrote: revoke all privs on the sequence to anyone but the user about to reset it reset it grant the options back Quoting the OP: That means, when others want to access the sequence between 31-Dec 23:59:55 and 1-Jan 00:00:05, they are waiting instead of getting an error. If you remove the privs, clients will get an error, unless I'm missing something. Good point. I'm guessing if you need a way to make other users wait, not get an error, you'll need to use a funtion with a security definer that will sleep or something during that period. hm. ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster Thanks for your help! Would you mind to give me an example on how to write this kind of function? -- Kathy Lo ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [GENERAL] Restart a sequence regularly
Kathy Lo wrote: On 11/21/07, Richard Huxton [EMAIL PROTECTED] wrote: You probably shouldn't attach any meaning to the numbers from a sequence - they're just guaranteed to be unique, nothing else. What you say here contradicts the following. Actually, the sequence is formed by 4-digit of year and 6-digit of sequence. So you *are* attaching significance to the number (by adding the current year to the front of it). So, it is required to change and restart the range of sequence at the beginning of every year. For example, at the beginning of 2008, the sequence should be changed to the range of 200801 - 200899 and restart at 200801. In the time of changing the sequence, it does not allow any users to get the unique number from this sequence. However, our staff don't want to do it manually because it is difficult for them to make sure no one accessing the sequence and our service cannot stop at that time. Therefore, I need to let the users to wait in the period of changing the sequence. Don't block users - have multiple sequences. If you define my_seq_2007, my_seq_2008, my_seq_2009 etc and then wrap access to them in a function you can EXTRACT() the year from the CURRENT_DATE and use that to form your per-year unique value. -- Richard Huxton Archonet Ltd ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
[GENERAL] Restart a sequence regularly
Hi, I am using Postgresql 8.0.3 in Fedora Core 4. In my database, it contains a sequence. And, I need to alter the range of this sequence and restart it to the start of the new range at 00:00:00 on 1st January on every year. 5 seconds before and after that time, I need to prevent users from calling nextval() to retrieve the next number from this sequence. I can write a Perl script to alter the sequence and schedule to run this script at 23:59:55 on 31st December on every year. But, I don't know how to lock the sequence to prevent others from accessing this sequence to get next number and Postgresql does not support to lock a sequence. How can I prevent others from accessing the sequence, like locking a table? That means, when others want to access the sequence between 31-Dec 23:59:55 and 1-Jan 00:00:05, they are waiting instead of getting an error. Thank -- Kathy Lo ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
