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* For update clause
@ 2010-06-15 19:42 Florence Cousin <[email protected]>
2010-06-15 20:04 ` Re: For update clause Bruce Momjian <[email protected]>
0 siblings, 1 reply; 4+ messages in thread
From: Florence Cousin @ 2010-06-15 19:42 UTC (permalink / raw)
To: pgsql-docs
Hi,
I am one of the french translators of the documentation. I am translating the
reference page of SELECT, but I fail to understand this sentence about the FOR
UPDATE clause ( http://www.postgresql.org/docs/9.0/static/sql-
select.html#SQL-FOR-UPDATE-SHARE )
---------------
In addition, rows that satisfied the query conditions as of the query snapshot
will be locked, although they will not be returned if they have since been
updated to not satisfy the query conditions.
------------------
Could anyone please explain it to me, so that I can translate it properly? A
word for word translation has really no meaning.
Florence
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: For update clause
2010-06-15 19:42 For update clause Florence Cousin <[email protected]>
@ 2010-06-15 20:04 ` Bruce Momjian <[email protected]>
2010-06-16 07:58 ` Re: For update clause Florence Cousin <[email protected]>
0 siblings, 1 reply; 4+ messages in thread
From: Bruce Momjian @ 2010-06-15 20:04 UTC (permalink / raw)
To: Florence Cousin <[email protected]>; +Cc: pgsql-docs
Florence Cousin wrote:
> Hi,
>
> I am one of the french translators of the documentation. I am translating the
> reference page of SELECT, but I fail to understand this sentence about the FOR
> UPDATE clause ( http://www.postgresql.org/docs/9.0/static/sql-
> select.html#SQL-FOR-UPDATE-SHARE )
>
> ---------------
> In addition, rows that satisfied the query conditions as of the query snapshot
> will be locked, although they will not be returned if they have since been
> updated to not satisfy the query conditions.
> ------------------
>
> Could anyone please explain it to me, so that I can translate it properly? A
> word for word translation has really no meaning.
Wow, that is a confusing double-negative sentence. I have updated the
text to be:
In addition, rows that satisfied the query conditions as of the
query snapshot will be locked, although they will not be returned
if they were updated after the snapshot and no longer satisfy the
query conditions.
What it is saying is that SELECT FOR UPDATE will lock all rows that
match the SELECT query using the current snapshot, but the returned rows
might be different because the rows were changed after the snapshot was
taken, and a SELECT FOR UPDATE will return the rows as UPDATE will see
them, which might not match the SELECT snapshot. Yeah, it is confusing.
--
Bruce Momjian <[email protected]> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ None of us is going to be here forever. +
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: For update clause
2010-06-15 19:42 For update clause Florence Cousin <[email protected]>
2010-06-15 20:04 ` Re: For update clause Bruce Momjian <[email protected]>
@ 2010-06-16 07:58 ` Florence Cousin <[email protected]>
2010-06-16 14:16 ` Re: For update clause Bruce Momjian <[email protected]>
0 siblings, 1 reply; 4+ messages in thread
From: Florence Cousin @ 2010-06-16 07:58 UTC (permalink / raw)
To: pgsql-docs
Le mardi 15 juin 2010 22:04:06, Bruce Momjian a écrit :
>
> Wow, that is a confusing double-negative sentence. I have updated the
> text to be:
>
> In addition, rows that satisfied the query conditions as of the
> query snapshot will be locked, although they will not be returned
> if they were updated after the snapshot and no longer satisfy the
> query conditions.
>
> What it is saying is that SELECT FOR UPDATE will lock all rows that
> match the SELECT query using the current snapshot, but the returned rows
> might be different because the rows were changed after the snapshot was
> taken, and a SELECT FOR UPDATE will return the rows as UPDATE will see
> them, which might not match the SELECT snapshot. Yeah, it is confusing.
Thank you for the patch and the explanation. It is clear for me now (the rows
returned are those that would be returned by an UPDATE, that is pretty
logical).
But I think most of the users will still not understand this, because they do
not know what a snapshot is, and do not really know how locking works.
And I managed to understand thank to the explanation, but I think I could not
understand with the new version of the explanation alone (the fact that rows
returned are the rows as UPDATE will see them)
Maybe it would be clearer with a longer explanation, or a link to an
explanation?
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: For update clause
2010-06-15 19:42 For update clause Florence Cousin <[email protected]>
2010-06-15 20:04 ` Re: For update clause Bruce Momjian <[email protected]>
2010-06-16 07:58 ` Re: For update clause Florence Cousin <[email protected]>
@ 2010-06-16 14:16 ` Bruce Momjian <[email protected]>
0 siblings, 0 replies; 4+ messages in thread
From: Bruce Momjian @ 2010-06-16 14:16 UTC (permalink / raw)
To: Florence Cousin <[email protected]>; +Cc: pgsql-docs
Florence Cousin wrote:
> Le mardi 15 juin 2010 22:04:06, Bruce Momjian a ?crit :
> >
> > Wow, that is a confusing double-negative sentence. I have updated the
> > text to be:
> >
> > In addition, rows that satisfied the query conditions as of the
> > query snapshot will be locked, although they will not be returned
> > if they were updated after the snapshot and no longer satisfy the
> > query conditions.
> >
> > What it is saying is that SELECT FOR UPDATE will lock all rows that
> > match the SELECT query using the current snapshot, but the returned rows
> > might be different because the rows were changed after the snapshot was
> > taken, and a SELECT FOR UPDATE will return the rows as UPDATE will see
> > them, which might not match the SELECT snapshot. Yeah, it is confusing.
>
> Thank you for the patch and the explanation. It is clear for me now (the rows
> returned are those that would be returned by an UPDATE, that is pretty
> logical).
>
> But I think most of the users will still not understand this, because they do
> not know what a snapshot is, and do not really know how locking works.
>
> And I managed to understand thank to the explanation, but I think I could not
> understand with the new version of the explanation alone (the fact that rows
> returned are the rows as UPDATE will see them)
>
> Maybe it would be clearer with a longer explanation, or a link to an
> explanation?
Well, the entire area is very complicated, but do we want to add even
more text there? I am not sure.
--
Bruce Momjian <[email protected]> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ None of us is going to be here forever. +
^ permalink raw reply [nested|flat] 4+ messages in thread
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2010-06-15 19:42 For update clause Florence Cousin <[email protected]>
2010-06-15 20:04 ` Bruce Momjian <[email protected]>
2010-06-16 07:58 ` Florence Cousin <[email protected]>
2010-06-16 14:16 ` Bruce Momjian <[email protected]>
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