Re: [GENERAL] Lock strategies!
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Hash: SHA1
Obviously depends on the carrier. Lloyds for example doesn't allow numbering
gaps. But as said: doing it in a fully isolated stored proc usually works.
The stp I use also assembles the alpha part, so I end up with something like
AA-0001234 in a fixed width format.
On Tuesday 25 November 2003 08:40 am, Marc A. Leith wrote:
Actually, in practice Policy Certificate 'numbers' only need to be
unique. Insurance companies (at least those we deal with) have no
restriction that there can be no holes. In fact, one of our clients has a
huge gap in the sequence.
Likewise - they aren't usually strictly numeric, consisting of ALPHA and
NUMERIC components. Ie. AA01 AA02 ... AA99 AB01.
A better example - is Invoice Numbers. Accountants hate the gaps, since
they leave room for fraud and make collection difficult.
That said - our implementation for unique ids is either use sequences or to
encapsulate the logic in a Stored Proc. and ensure that these tranasactions
are fully isolated.
Marc A. Leith
redboxdata inc.
E-mail:[EMAIL PROTECTED]
Quoting Uwe C. Schroeder [EMAIL PROTECTED]:
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Hash: SHA1
On Monday 24 November 2003 08:01 am, Dave Cramer wrote:
Marcelo,
You are asking for the impossible.
In order for sequences to work reliably they have to exist outside of a
transaction, and be atomic. If two transactions asked for a sequence
simultaneously, what number would you give them? If the first one gets
1, and the second gets 2 how do you roll back the first one and then
give the second one 1?
And it gets worse, what happens if 10 connections ask for one
simultaneously and then connection 3 7 rollback?
I don't know how to say this gently, but usually this requirement
suggests that more thinking is required on the application end.
Well, there are cases where you have to have the numbers without holes -
no matter what. It's not even a matter of the application. Go check your
insurance policy: the policy numbers are sequential without holes.
Actually you can make that work via stored procedures. But you'd have to
lock the table exclusive to avoid duplicates. This still might produce
numbering gaps,
but you can have the application compensate for that, i.e. if you have a
rollback remember the number someplace else and reuse it for the next
record.
Dave
On Mon, 2003-11-24 at 10:48, MaRcElO PeReIrA wrote:
Dave,
I actually use just the sequence, as you wrote!
The biggest problem it that I *can't* have holes in
that column, so it was because I used id (serial) and
forn_id (integer).
All other tables use only the sequence by itself, but
this one, especially, CAN'T have holes! It is the
problem!!! ;-)
So, if I rollback or whatever, the ID will be
populated with the sequence values, but the forn_id
must increase in a controled way, ie, without holes!
Advices??
Regards!
Marcelo
--- Dave Cramer [EMAIL PROTECTED] escreveu:
Marceio
The sequence logic takes care of it. try it yourself
open two connections with psql
on one do a
begin;
insert into table
select curval('forn_id_seq');
on the other
do a
begin
insert into table
select curval('forn_id_seq');
You will see that they both increment the sequence
number
you will also see how to get the current value as
well.
Note, no locking is actually required, you can do
this without the
transaction stuff, it is there just so you can see
it in two sessions at
the same time.
Also note that a rollback will NOT roll back the
sequence number, this
will end up with holes but sequences are not
guaranteed to not have
holes.
Why do you have two columns, id, and forn_id, you
only need one.
and then do an
insert into forn (descrip) values ( 'some
description' );
then select curval('forn_id_seq');
forn_id will be populated for you with the value
from curval.
Dave
On Mon, 2003-11-24 at 08:20, MaRcElO PeReIrA wrote:
Hi guys,
I have a simple table:
teste=# \d forn
Table public.forn
Column | Type |
Modifiers
-+-+-
-
id | integer | not null default
nextval('public.forn_id_seq'::text)
forn_id | integer |
descrip | text|
Ok! The forn_id is supposed to be sequencial and
without holes (if someone perform a DELETE or
UPDATE,
so there will be a hole... no problem if the hole
happens in this case!).
Well, to know
Re: [GENERAL] Lock strategies!
How can you avoid holes?
Unless you void policies that people cancel halfway through the process
? How is that different than rollback?
Lets say that the customer goes through the motions and after signing
the papers, and then during the cooling off period (mandatory in Canada)
decides he really doesn't want the policy (rollback). A policy number
must have been assigned. So now we have a hole ?
Dave
On Tue, 2003-11-25 at 19:07, Uwe C. Schroeder wrote:
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1
Obviously depends on the carrier. Lloyds for example doesn't allow numbering
gaps. But as said: doing it in a fully isolated stored proc usually works.
The stp I use also assembles the alpha part, so I end up with something like
AA-0001234 in a fixed width format.
On Tuesday 25 November 2003 08:40 am, Marc A. Leith wrote:
Actually, in practice Policy Certificate 'numbers' only need to be
unique. Insurance companies (at least those we deal with) have no
restriction that there can be no holes. In fact, one of our clients has a
huge gap in the sequence.
Likewise - they aren't usually strictly numeric, consisting of ALPHA and
NUMERIC components. Ie. AA01 AA02 ... AA99 AB01.
A better example - is Invoice Numbers. Accountants hate the gaps, since
they leave room for fraud and make collection difficult.
That said - our implementation for unique ids is either use sequences or to
encapsulate the logic in a Stored Proc. and ensure that these tranasactions
are fully isolated.
Marc A. Leith
redboxdata inc.
E-mail:[EMAIL PROTECTED]
Quoting Uwe C. Schroeder [EMAIL PROTECTED]:
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Hash: SHA1
On Monday 24 November 2003 08:01 am, Dave Cramer wrote:
Marcelo,
You are asking for the impossible.
In order for sequences to work reliably they have to exist outside of a
transaction, and be atomic. If two transactions asked for a sequence
simultaneously, what number would you give them? If the first one gets
1, and the second gets 2 how do you roll back the first one and then
give the second one 1?
And it gets worse, what happens if 10 connections ask for one
simultaneously and then connection 3 7 rollback?
I don't know how to say this gently, but usually this requirement
suggests that more thinking is required on the application end.
Well, there are cases where you have to have the numbers without holes -
no matter what. It's not even a matter of the application. Go check your
insurance policy: the policy numbers are sequential without holes.
Actually you can make that work via stored procedures. But you'd have to
lock the table exclusive to avoid duplicates. This still might produce
numbering gaps,
but you can have the application compensate for that, i.e. if you have a
rollback remember the number someplace else and reuse it for the next
record.
Dave
On Mon, 2003-11-24 at 10:48, MaRcElO PeReIrA wrote:
Dave,
I actually use just the sequence, as you wrote!
The biggest problem it that I *can't* have holes in
that column, so it was because I used id (serial) and
forn_id (integer).
All other tables use only the sequence by itself, but
this one, especially, CAN'T have holes! It is the
problem!!! ;-)
So, if I rollback or whatever, the ID will be
populated with the sequence values, but the forn_id
must increase in a controled way, ie, without holes!
Advices??
Regards!
Marcelo
--- Dave Cramer [EMAIL PROTECTED] escreveu:
Marceio
The sequence logic takes care of it. try it yourself
open two connections with psql
on one do a
begin;
insert into table
select curval('forn_id_seq');
on the other
do a
begin
insert into table
select curval('forn_id_seq');
You will see that they both increment the sequence
number
you will also see how to get the current value as
well.
Note, no locking is actually required, you can do
this without the
transaction stuff, it is there just so you can see
it in two sessions at
the same time.
Also note that a rollback will NOT roll back the
sequence number, this
will end up with holes but sequences are not
guaranteed to not have
holes.
Why do you have two columns, id, and forn_id, you
only need one.
and then do an
insert into forn (descrip) values ( 'some
description' );
then select curval('forn_id_seq');
forn_id will be populated for you with the value
from curval.
Dave
On Mon, 2003-11-24 at 08:20, MaRcElO PeReIrA wrote:
Hi guys,
I have a simple
Re: [GENERAL] Lock strategies!
It seems to me there is a confusion about identifiers. There is the primary
key of the table which should be a sequence and may have holes. Seperate
from that is the CustomerFriendlyID which is an ID you can assign and
reassign at your leasure. For a bank, the statement numbers all start from one
for each customer so they're not useful as a global identifier anyway.
In your case below, once you've signed the paper-work, the policy is a legal
document and would need to be kept even if it never was activated.
IMHO, most people looking for no-hole-sequences are using the primary keys
for Bad Things (tm).
Hope this helps,
On Tue, Nov 25, 2003 at 10:19:20PM -0500, Dave Cramer wrote:
How can you avoid holes?
Unless you void policies that people cancel halfway through the process
? How is that different than rollback?
Lets say that the customer goes through the motions and after signing
the papers, and then during the cooling off period (mandatory in Canada)
decides he really doesn't want the policy (rollback). A policy number
must have been assigned. So now we have a hole ?
Dave
On Tue, 2003-11-25 at 19:07, Uwe C. Schroeder wrote:
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1
Obviously depends on the carrier. Lloyds for example doesn't allow numbering
gaps. But as said: doing it in a fully isolated stored proc usually works.
The stp I use also assembles the alpha part, so I end up with something like
AA-0001234 in a fixed width format.
On Tuesday 25 November 2003 08:40 am, Marc A. Leith wrote:
Actually, in practice Policy Certificate 'numbers' only need to be
unique. Insurance companies (at least those we deal with) have no
restriction that there can be no holes. In fact, one of our clients has a
huge gap in the sequence.
Likewise - they aren't usually strictly numeric, consisting of ALPHA and
NUMERIC components. Ie. AA01 AA02 ... AA99 AB01.
A better example - is Invoice Numbers. Accountants hate the gaps, since
they leave room for fraud and make collection difficult.
That said - our implementation for unique ids is either use sequences or to
encapsulate the logic in a Stored Proc. and ensure that these tranasactions
are fully isolated.
Marc A. Leith
redboxdata inc.
E-mail:[EMAIL PROTECTED]
Quoting Uwe C. Schroeder [EMAIL PROTECTED]:
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1
On Monday 24 November 2003 08:01 am, Dave Cramer wrote:
Marcelo,
You are asking for the impossible.
In order for sequences to work reliably they have to exist outside of a
transaction, and be atomic. If two transactions asked for a sequence
simultaneously, what number would you give them? If the first one gets
1, and the second gets 2 how do you roll back the first one and then
give the second one 1?
And it gets worse, what happens if 10 connections ask for one
simultaneously and then connection 3 7 rollback?
I don't know how to say this gently, but usually this requirement
suggests that more thinking is required on the application end.
Well, there are cases where you have to have the numbers without holes -
no matter what. It's not even a matter of the application. Go check your
insurance policy: the policy numbers are sequential without holes.
Actually you can make that work via stored procedures. But you'd have to
lock the table exclusive to avoid duplicates. This still might produce
numbering gaps,
but you can have the application compensate for that, i.e. if you have a
rollback remember the number someplace else and reuse it for the next
record.
Dave
On Mon, 2003-11-24 at 10:48, MaRcElO PeReIrA wrote:
Dave,
I actually use just the sequence, as you wrote!
The biggest problem it that I *can't* have holes in
that column, so it was because I used id (serial) and
forn_id (integer).
All other tables use only the sequence by itself, but
this one, especially, CAN'T have holes! It is the
problem!!! ;-)
So, if I rollback or whatever, the ID will be
populated with the sequence values, but the forn_id
must increase in a controled way, ie, without holes!
Advices??
Regards!
Marcelo
--- Dave Cramer [EMAIL PROTECTED] escreveu:
Marceio
The sequence logic takes care of it. try it yourself
open two connections with psql
on one do a
begin;
insert into table
select curval('forn_id_seq');
on the other
do a
begin
insert into table
select curval('forn_id_seq');
You will see that they both increment the sequence
number
you will also see how to get the current value as
well.
Re: [GENERAL] Lock strategies!
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Actually in this case you don't have a hole. Yes you created the next policy (in this case, may be any similar situation). But the customer already signed the contract. This means even if he opts out of it, a record has to be kept. In some areas this is even a legal requirement. So you don't rollback, you just mark the record as inactive cancelled or whatever the situation stipulates. In case of a commercial insurance policy in California most likely the customer would have to pay a penalty - usually a percentage of the premium - so you have to keep the record. You also may want to keep the record to deny further requests from this customer, or to simply warn the customer rep that this customer is a drop out type. So it's not a gap in the numbering. As Martijn already pointed out: don't confuse this with an internal record sequence, which you should never ever give to the user as an id or something. The requirement for record sequences (usually the primary key or part of it) is uniqueness. On Tuesday 25 November 2003 07:19 pm, Dave Cramer wrote: How can you avoid holes? Unless you void policies that people cancel halfway through the process ? How is that different than rollback? Lets say that the customer goes through the motions and after signing the papers, and then during the cooling off period (mandatory in Canada) decides he really doesn't want the policy (rollback). A policy number must have been assigned. So now we have a hole ? Dave On Tue, 2003-11-25 at 19:07, Uwe C. Schroeder wrote: -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Obviously depends on the carrier. Lloyds for example doesn't allow numbering gaps. But as said: doing it in a fully isolated stored proc usually works. The stp I use also assembles the alpha part, so I end up with something like AA-0001234 in a fixed width format. On Tuesday 25 November 2003 08:40 am, Marc A. Leith wrote: Actually, in practice Policy Certificate 'numbers' only need to be unique. Insurance companies (at least those we deal with) have no restriction that there can be no holes. In fact, one of our clients has a huge gap in the sequence. Likewise - they aren't usually strictly numeric, consisting of ALPHA and NUMERIC components. Ie. AA01 AA02 ... AA99 AB01. A better example - is Invoice Numbers. Accountants hate the gaps, since they leave room for fraud and make collection difficult. That said - our implementation for unique ids is either use sequences or to encapsulate the logic in a Stored Proc. and ensure that these tranasactions are fully isolated. Marc A. Leith redboxdata inc. E-mail:[EMAIL PROTECTED] Quoting Uwe C. Schroeder [EMAIL PROTECTED]: -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Monday 24 November 2003 08:01 am, Dave Cramer wrote: Marcelo, You are asking for the impossible. In order for sequences to work reliably they have to exist outside of a transaction, and be atomic. If two transactions asked for a sequence simultaneously, what number would you give them? If the first one gets 1, and the second gets 2 how do you roll back the first one and then give the second one 1? And it gets worse, what happens if 10 connections ask for one simultaneously and then connection 3 7 rollback? I don't know how to say this gently, but usually this requirement suggests that more thinking is required on the application end. Well, there are cases where you have to have the numbers without holes - no matter what. It's not even a matter of the application. Go check your insurance policy: the policy numbers are sequential without holes. Actually you can make that work via stored procedures. But you'd have to lock the table exclusive to avoid duplicates. This still might produce numbering gaps, but you can have the application compensate for that, i.e. if you have a rollback remember the number someplace else and reuse it for the next record. Dave On Mon, 2003-11-24 at 10:48, MaRcElO PeReIrA wrote: Dave, I actually use just the sequence, as you wrote! The biggest problem it that I *can't* have holes in that column, so it was because I used id (serial) and forn_id (integer). All other tables use only the sequence by itself, but this one, especially, CAN'T have holes! It is the problem!!! ;-) So, if I rollback or whatever, the ID will be populated with the sequence values, but the forn_id must increase in a controled way, ie, without holes! Advices?? Regards! Marcelo --- Dave Cramer [EMAIL PROTECTED] escreveu: Marceio The sequence logic takes care of it. try it yourself
Re: [GENERAL] Lock strategies!
I think that defining forn_id as serial is what you are looking for.
This will handle the assignment of unique numbers to the id for you (it creates
a sequence table).
The locking stategy is fraught with danger... and unnecessary.
Marc A. Leith
redboxdata inc.
E-mail:[EMAIL PROTECTED]
Quoting MaRcElO PeReIrA [EMAIL PROTECTED]:
Hi guys,
I have a simple table:
teste=# \d forn
Table public.forn
Column | Type | Modifiers
-+-+--
id | integer | not null default
nextval('public.forn_id_seq'::text)
forn_id | integer |
descrip | text|
Ok! The forn_id is supposed to be sequencial and
without holes (if someone perform a DELETE or UPDATE,
so there will be a hole... no problem if the hole
happens in this case!).
Well, to know the next value of the forn_id column, it
was planned to be done like this:
teste=# INSERT INTO forn (forn_id,descrip) VALUES
((SELECT max(forn_id) FROM forn),'descrip1');
It will cause a huge delay in case this table became
huge, because the forn_id isn't an indexed column (but
I would index it! The problem I am talking about is
ONLY about the sequence of numbers).
As a way to be sure it will not another other client
getting the exact value as the max(forn_id), there was
a dirty thing:
teste=# BEGIN;
teste=# LOCK TABLE forn IN ACCESS EXCLUSIVE MODE;
teste=# INSERT INTO ...
teste=# COMMIT;
Well, I really think it is not the best way to do that
and I am asking you for advices!
1) Is it (... max(forn_id)... ) the best way to get
the next value to be inserted in the table?
2) Is there a automatic way to do that?
Thanks in advance and
Best Regards,
Marcelo
__
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Re: [GENERAL] Lock strategies!
Dave,
I actually use just the sequence, as you wrote!
The biggest problem it that I *can't* have holes in
that column, so it was because I used id (serial) and
forn_id (integer).
All other tables use only the sequence by itself, but
this one, especially, CAN'T have holes! It is the
problem!!! ;-)
So, if I rollback or whatever, the ID will be
populated with the sequence values, but the forn_id
must increase in a controled way, ie, without holes!
Advices??
Regards!
Marcelo
--- Dave Cramer [EMAIL PROTECTED] escreveu:
Marceio
The sequence logic takes care of it. try it yourself
open two connections with psql
on one do a
begin;
insert into table
select curval('forn_id_seq');
on the other
do a
begin
insert into table
select curval('forn_id_seq');
You will see that they both increment the sequence
number
you will also see how to get the current value as
well.
Note, no locking is actually required, you can do
this without the
transaction stuff, it is there just so you can see
it in two sessions at
the same time.
Also note that a rollback will NOT roll back the
sequence number, this
will end up with holes but sequences are not
guaranteed to not have
holes.
Why do you have two columns, id, and forn_id, you
only need one.
and then do an
insert into forn (descrip) values ( 'some
description' );
then select curval('forn_id_seq');
forn_id will be populated for you with the value
from curval.
Dave
On Mon, 2003-11-24 at 08:20, MaRcElO PeReIrA wrote:
Hi guys,
I have a simple table:
teste=# \d forn
Table public.forn
Column | Type |
Modifiers
-+-+--
id | integer | not null default
nextval('public.forn_id_seq'::text)
forn_id | integer |
descrip | text|
Ok! The forn_id is supposed to be sequencial and
without holes (if someone perform a DELETE or
UPDATE,
so there will be a hole... no problem if the hole
happens in this case!).
Well, to know the next value of the forn_id
column, it
was planned to be done like this:
teste=# INSERT INTO forn (forn_id,descrip) VALUES
((SELECT max(forn_id) FROM forn),'descrip1');
It will cause a huge delay in case this table
became
huge, because the forn_id isn't an indexed column
(but
I would index it! The problem I am talking about
is
ONLY about the sequence of numbers).
As a way to be sure it will not another other
client
getting the exact value as the max(forn_id), there
was
a dirty thing:
teste=# BEGIN;
teste=# LOCK TABLE forn IN ACCESS EXCLUSIVE MODE;
teste=# INSERT INTO ...
teste=# COMMIT;
Well, I really think it is not the best way to do
that
and I am asking you for advices!
1) Is it (... max(forn_id)... ) the best way to
get
the next value to be inserted in the table?
2) Is there a automatic way to do that?
Thanks in advance and
Best Regards,
Marcelo
__
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Re: [GENERAL] Lock strategies!
Marceio
The sequence logic takes care of it. try it yourself
open two connections with psql
on one do a
begin;
insert into table
select curval('forn_id_seq');
on the other
do a
begin
insert into table
select curval('forn_id_seq');
You will see that they both increment the sequence number
you will also see how to get the current value as well.
Note, no locking is actually required, you can do this without the
transaction stuff, it is there just so you can see it in two sessions at
the same time.
Also note that a rollback will NOT roll back the sequence number, this
will end up with holes but sequences are not guaranteed to not have
holes.
Why do you have two columns, id, and forn_id, you only need one.
and then do an
insert into forn (descrip) values ( 'some description' );
then select curval('forn_id_seq');
forn_id will be populated for you with the value from curval.
Dave
On Mon, 2003-11-24 at 08:20, MaRcElO PeReIrA wrote:
Hi guys,
I have a simple table:
teste=# \d forn
Table public.forn
Column | Type | Modifiers
-+-+--
id | integer | not null default
nextval('public.forn_id_seq'::text)
forn_id | integer |
descrip | text|
Ok! The forn_id is supposed to be sequencial and
without holes (if someone perform a DELETE or UPDATE,
so there will be a hole... no problem if the hole
happens in this case!).
Well, to know the next value of the forn_id column, it
was planned to be done like this:
teste=# INSERT INTO forn (forn_id,descrip) VALUES
((SELECT max(forn_id) FROM forn),'descrip1');
It will cause a huge delay in case this table became
huge, because the forn_id isn't an indexed column (but
I would index it! The problem I am talking about is
ONLY about the sequence of numbers).
As a way to be sure it will not another other client
getting the exact value as the max(forn_id), there was
a dirty thing:
teste=# BEGIN;
teste=# LOCK TABLE forn IN ACCESS EXCLUSIVE MODE;
teste=# INSERT INTO ...
teste=# COMMIT;
Well, I really think it is not the best way to do that
and I am asking you for advices!
1) Is it (... max(forn_id)... ) the best way to get
the next value to be inserted in the table?
2) Is there a automatic way to do that?
Thanks in advance and
Best Regards,
Marcelo
__
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Re: [GENERAL] Lock strategies!
On Mon, 24 Nov 2003 10:20:07 -0300 (ART)
MaRcElO PeReIrA [EMAIL PROTECTED] wrote:
Hi guys,
I have a simple table:
teste=# \d forn
Table public.forn
Column | Type | Modifiers
-+-+-
-
id | integer | not null default
nextval('public.forn_id_seq'::text)
forn_id | integer |
descrip | text|
Why not make forn_id a sequence as well?
then you simply call nextval('forn_id_seq')
--
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http://www.stuarthamm.net/
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Re: [GENERAL] Lock strategies!
Marcelo,
You are asking for the impossible.
In order for sequences to work reliably they have to exist outside of a
transaction, and be atomic. If two transactions asked for a sequence
simultaneously, what number would you give them? If the first one gets
1, and the second gets 2 how do you roll back the first one and then
give the second one 1?
And it gets worse, what happens if 10 connections ask for one
simultaneously and then connection 3 7 rollback?
I don't know how to say this gently, but usually this requirement
suggests that more thinking is required on the application end.
Dave
On Mon, 2003-11-24 at 10:48, MaRcElO PeReIrA wrote:
Dave,
I actually use just the sequence, as you wrote!
The biggest problem it that I *can't* have holes in
that column, so it was because I used id (serial) and
forn_id (integer).
All other tables use only the sequence by itself, but
this one, especially, CAN'T have holes! It is the
problem!!! ;-)
So, if I rollback or whatever, the ID will be
populated with the sequence values, but the forn_id
must increase in a controled way, ie, without holes!
Advices??
Regards!
Marcelo
--- Dave Cramer [EMAIL PROTECTED] escreveu:
Marceio
The sequence logic takes care of it. try it yourself
open two connections with psql
on one do a
begin;
insert into table
select curval('forn_id_seq');
on the other
do a
begin
insert into table
select curval('forn_id_seq');
You will see that they both increment the sequence
number
you will also see how to get the current value as
well.
Note, no locking is actually required, you can do
this without the
transaction stuff, it is there just so you can see
it in two sessions at
the same time.
Also note that a rollback will NOT roll back the
sequence number, this
will end up with holes but sequences are not
guaranteed to not have
holes.
Why do you have two columns, id, and forn_id, you
only need one.
and then do an
insert into forn (descrip) values ( 'some
description' );
then select curval('forn_id_seq');
forn_id will be populated for you with the value
from curval.
Dave
On Mon, 2003-11-24 at 08:20, MaRcElO PeReIrA wrote:
Hi guys,
I have a simple table:
teste=# \d forn
Table public.forn
Column | Type |
Modifiers
-+-+--
id | integer | not null default
nextval('public.forn_id_seq'::text)
forn_id | integer |
descrip | text|
Ok! The forn_id is supposed to be sequencial and
without holes (if someone perform a DELETE or
UPDATE,
so there will be a hole... no problem if the hole
happens in this case!).
Well, to know the next value of the forn_id
column, it
was planned to be done like this:
teste=# INSERT INTO forn (forn_id,descrip) VALUES
((SELECT max(forn_id) FROM forn),'descrip1');
It will cause a huge delay in case this table
became
huge, because the forn_id isn't an indexed column
(but
I would index it! The problem I am talking about
is
ONLY about the sequence of numbers).
As a way to be sure it will not another other
client
getting the exact value as the max(forn_id), there
was
a dirty thing:
teste=# BEGIN;
teste=# LOCK TABLE forn IN ACCESS EXCLUSIVE MODE;
teste=# INSERT INTO ...
teste=# COMMIT;
Well, I really think it is not the best way to do
that
and I am asking you for advices!
1) Is it (... max(forn_id)... ) the best way to
get
the next value to be inserted in the table?
2) Is there a automatic way to do that?
Thanks in advance and
Best Regards,
Marcelo
__
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Re: [GENERAL] Lock strategies!
Hi Dave, Marc and all others,
I know it is really weird!
But, how can I explain to the user, who use the
sequence numbers, that he will have to handle with
those holes?
Ok! I will try to handle the holes! (fight against the
users)
Thanks!
Marcelo
--- Dave Cramer [EMAIL PROTECTED] escreveu:
Marcelo,
You are asking for the impossible.
In order for sequences to work reliably they have to
exist outside of a
transaction, and be atomic. If two transactions
asked for a sequence
simultaneously, what number would you give them? If
the first one gets
1, and the second gets 2 how do you roll back the
first one and then
give the second one 1?
And it gets worse, what happens if 10 connections
ask for one
simultaneously and then connection 3 7 rollback?
I don't know how to say this gently, but usually
this requirement
suggests that more thinking is required on the
application end.
Dave
On Mon, 2003-11-24 at 10:48, MaRcElO PeReIrA wrote:
Dave,
I actually use just the sequence, as you wrote!
The biggest problem it that I *can't* have holes
in
that column, so it was because I used id (serial)
and
forn_id (integer).
All other tables use only the sequence by itself,
but
this one, especially, CAN'T have holes! It is the
problem!!! ;-)
So, if I rollback or whatever, the ID will be
populated with the sequence values, but the
forn_id
must increase in a controled way, ie, without
holes!
Advices??
Regards!
Marcelo
--- Dave Cramer [EMAIL PROTECTED] escreveu:
Marceio
The sequence logic takes care of it. try it
yourself
open two connections with psql
on one do a
begin;
insert into table
select curval('forn_id_seq');
on the other
do a
begin
insert into table
select curval('forn_id_seq');
You will see that they both increment the
sequence
number
you will also see how to get the current value
as
well.
Note, no locking is actually required, you can
do
this without the
transaction stuff, it is there just so you can
see
it in two sessions at
the same time.
Also note that a rollback will NOT roll back the
sequence number, this
will end up with holes but sequences are not
guaranteed to not have
holes.
Why do you have two columns, id, and forn_id,
you
only need one.
and then do an
insert into forn (descrip) values ( 'some
description' );
then select curval('forn_id_seq');
forn_id will be populated for you with the value
from curval.
Dave
On Mon, 2003-11-24 at 08:20, MaRcElO PeReIrA
wrote:
Hi guys,
I have a simple table:
teste=# \d forn
Table public.forn
Column | Type |
Modifiers
-+-+--
id | integer | not null default
nextval('public.forn_id_seq'::text)
forn_id | integer |
descrip | text|
Ok! The forn_id is supposed to be sequencial
and
without holes (if someone perform a DELETE or
UPDATE,
so there will be a hole... no problem if the
hole
happens in this case!).
Well, to know the next value of the forn_id
column, it
was planned to be done like this:
teste=# INSERT INTO forn (forn_id,descrip)
VALUES
((SELECT max(forn_id) FROM forn),'descrip1');
It will cause a huge delay in case this table
became
huge, because the forn_id isn't an indexed
column
(but
I would index it! The problem I am talking
about
is
ONLY about the sequence of numbers).
As a way to be sure it will not another other
client
getting the exact value as the max(forn_id),
there
was
a dirty thing:
teste=# BEGIN;
teste=# LOCK TABLE forn IN ACCESS EXCLUSIVE
MODE;
teste=# INSERT INTO ...
teste=# COMMIT;
Well, I really think it is not the best way to
do
that
and I am asking you for advices!
1) Is it (... max(forn_id)... ) the best way
to
get
the next value to be inserted in the table?
2) Is there a automatic way to do that?
Thanks in advance and
Best Regards,
Marcelo
__
Yahoo! Mail: 6MB, anti-spam e antivírus
gratuito!
Crie sua conta agora:
http://mail.yahoo.com.br
=== message truncated ===
Yahoo! Mail - 6MB, anti-spam e antivírus gratuito. Crie sua conta agora:
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TIP 7: don't forget to increase your free space map settings
Re: [GENERAL] Lock strategies!
On Mon, 24 Nov 2003 12:48:26 -0300 (ART) MaRcElO PeReIrA [EMAIL PROTECTED] wrote: The biggest problem it that I *can't* have holes in that column, so it was because I used id (serial) and forn_id (integer). Well, if you cannot use a sequence you will have no choice but to use locking. don't use max - it isn't fast on PG use select forn_id from thetable order by fornid desc limit 1. You'll need an index on forn_id or performance will suffer. -- Jeff Trout [EMAIL PROTECTED] http://www.jefftrout.com/ http://www.stuarthamm.net/ ---(end of broadcast)--- TIP 9: the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [GENERAL] Lock strategies!
Perhaps the primary key should be a sequence/serial, but also have a
secondary key which is assigned after commit.
You could have a process that continually ran something like:
select max(skey) from the_table;
select pkey from the_table where skey is null;
Then loop through the answers and assign sequenctial values.
As long as this is the only process that is allowed to update skey, it
should work.
Jon
On 24 Nov 2003, Dave Cramer wrote:
Marcelo,
You are asking for the impossible.
In order for sequences to work reliably they have to exist outside of a
transaction, and be atomic. If two transactions asked for a sequence
simultaneously, what number would you give them? If the first one gets
1, and the second gets 2 how do you roll back the first one and then
give the second one 1?
And it gets worse, what happens if 10 connections ask for one
simultaneously and then connection 3 7 rollback?
I don't know how to say this gently, but usually this requirement
suggests that more thinking is required on the application end.
Dave
On Mon, 2003-11-24 at 10:48, MaRcElO PeReIrA wrote:
Dave,
I actually use just the sequence, as you wrote!
The biggest problem it that I *can't* have holes in
that column, so it was because I used id (serial) and
forn_id (integer).
All other tables use only the sequence by itself, but
this one, especially, CAN'T have holes! It is the
problem!!! ;-)
So, if I rollback or whatever, the ID will be
populated with the sequence values, but the forn_id
must increase in a controled way, ie, without holes!
Advices??
Regards!
Marcelo
--- Dave Cramer [EMAIL PROTECTED] escreveu:
Marceio
The sequence logic takes care of it. try it yourself
open two connections with psql
on one do a
begin;
insert into table
select curval('forn_id_seq');
on the other
do a
begin
insert into table
select curval('forn_id_seq');
You will see that they both increment the sequence
number
you will also see how to get the current value as
well.
Note, no locking is actually required, you can do
this without the
transaction stuff, it is there just so you can see
it in two sessions at
the same time.
Also note that a rollback will NOT roll back the
sequence number, this
will end up with holes but sequences are not
guaranteed to not have
holes.
Why do you have two columns, id, and forn_id, you
only need one.
and then do an
insert into forn (descrip) values ( 'some
description' );
then select curval('forn_id_seq');
forn_id will be populated for you with the value
from curval.
Dave
On Mon, 2003-11-24 at 08:20, MaRcElO PeReIrA wrote:
Hi guys,
I have a simple table:
teste=# \d forn
Table public.forn
Column | Type |
Modifiers
-+-+--
id | integer | not null default
nextval('public.forn_id_seq'::text)
forn_id | integer |
descrip | text|
Ok! The forn_id is supposed to be sequencial and
without holes (if someone perform a DELETE or
UPDATE,
so there will be a hole... no problem if the hole
happens in this case!).
Well, to know the next value of the forn_id
column, it
was planned to be done like this:
teste=# INSERT INTO forn (forn_id,descrip) VALUES
((SELECT max(forn_id) FROM forn),'descrip1');
It will cause a huge delay in case this table
became
huge, because the forn_id isn't an indexed column
(but
I would index it! The problem I am talking about
is
ONLY about the sequence of numbers).
As a way to be sure it will not another other
client
getting the exact value as the max(forn_id), there
was
a dirty thing:
teste=# BEGIN;
teste=# LOCK TABLE forn IN ACCESS EXCLUSIVE MODE;
teste=# INSERT INTO ...
teste=# COMMIT;
Well, I really think it is not the best way to do
that
and I am asking you for advices!
1) Is it (... max(forn_id)... ) the best way to
get
the next value to be inserted in the table?
2) Is there a automatic way to do that?
Thanks in advance and
Best Regards,
Marcelo
__
Yahoo! Mail: 6MB, anti-spam e antivírus gratuito!
Crie sua conta agora:
http://mail.yahoo.com.br
---(end of
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TIP 4: Don't 'kill -9' the postmaster
__
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TIP 4: Don't
Re: [GENERAL] Lock strategies!
But, how can I explain to the user, who use the
sequence numbers, that he will have to handle with
those holes?
If it's just hte user, you might try to make sure that there are ALWAYS
holes, so he doesn't get confused.
Jon
Ok! I will try to handle the holes! (fight against the
users)
Thanks!
Marcelo
--- Dave Cramer [EMAIL PROTECTED] escreveu:
Marcelo,
You are asking for the impossible.
In order for sequences to work reliably they have to
exist outside of a
transaction, and be atomic. If two transactions
asked for a sequence
simultaneously, what number would you give them? If
the first one gets
1, and the second gets 2 how do you roll back the
first one and then
give the second one 1?
And it gets worse, what happens if 10 connections
ask for one
simultaneously and then connection 3 7 rollback?
I don't know how to say this gently, but usually
this requirement
suggests that more thinking is required on the
application end.
Dave
On Mon, 2003-11-24 at 10:48, MaRcElO PeReIrA wrote:
Dave,
I actually use just the sequence, as you wrote!
The biggest problem it that I *can't* have holes
in
that column, so it was because I used id (serial)
and
forn_id (integer).
All other tables use only the sequence by itself,
but
this one, especially, CAN'T have holes! It is the
problem!!! ;-)
So, if I rollback or whatever, the ID will be
populated with the sequence values, but the
forn_id
must increase in a controled way, ie, without
holes!
Advices??
Regards!
Marcelo
--- Dave Cramer [EMAIL PROTECTED] escreveu:
Marceio
The sequence logic takes care of it. try it
yourself
open two connections with psql
on one do a
begin;
insert into table
select curval('forn_id_seq');
on the other
do a
begin
insert into table
select curval('forn_id_seq');
You will see that they both increment the
sequence
number
you will also see how to get the current value
as
well.
Note, no locking is actually required, you can
do
this without the
transaction stuff, it is there just so you can
see
it in two sessions at
the same time.
Also note that a rollback will NOT roll back the
sequence number, this
will end up with holes but sequences are not
guaranteed to not have
holes.
Why do you have two columns, id, and forn_id,
you
only need one.
and then do an
insert into forn (descrip) values ( 'some
description' );
then select curval('forn_id_seq');
forn_id will be populated for you with the value
from curval.
Dave
On Mon, 2003-11-24 at 08:20, MaRcElO PeReIrA
wrote:
Hi guys,
I have a simple table:
teste=# \d forn
Table public.forn
Column | Type |
Modifiers
-+-+--
id | integer | not null default
nextval('public.forn_id_seq'::text)
forn_id | integer |
descrip | text|
Ok! The forn_id is supposed to be sequencial
and
without holes (if someone perform a DELETE or
UPDATE,
so there will be a hole... no problem if the
hole
happens in this case!).
Well, to know the next value of the forn_id
column, it
was planned to be done like this:
teste=# INSERT INTO forn (forn_id,descrip)
VALUES
((SELECT max(forn_id) FROM forn),'descrip1');
It will cause a huge delay in case this table
became
huge, because the forn_id isn't an indexed
column
(but
I would index it! The problem I am talking
about
is
ONLY about the sequence of numbers).
As a way to be sure it will not another other
client
getting the exact value as the max(forn_id),
there
was
a dirty thing:
teste=# BEGIN;
teste=# LOCK TABLE forn IN ACCESS EXCLUSIVE
MODE;
teste=# INSERT INTO ...
teste=# COMMIT;
Well, I really think it is not the best way to
do
that
and I am asking you for advices!
1) Is it (... max(forn_id)... ) the best way
to
get
the next value to be inserted in the table?
2) Is there a automatic way to do that?
Thanks in advance and
Best Regards,
Marcelo
__
Yahoo! Mail: 6MB, anti-spam e antivírus
gratuito!
Crie sua conta agora:
http://mail.yahoo.com.br
=== message truncated ===
Yahoo! Mail - 6MB, anti-spam e antivírus gratuito. Crie sua conta agora:
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TIP 7: don't forget to increase your free space
