On Mon, Nov 11, 2013 at 08:59:35PM -0500, Tom Lane wrote:
> Bruce Momjian <[email protected]> writes:
> > On Mon, Nov 11, 2013 at 03:39:45PM -0500, Tom Lane wrote:
> >> I'm not really seeing the point of s/transaction/session/ here.
>
> > Well, the problem with the original wording is that we don't take a new
> > snapshot for every transaction in the default read-committed mode.
>
> We take at least one snapshot per transaction, in any mode. Referring
> to sessions makes it even further away from being a useful concept.
>
> > Would you prefer I refer to statements, e.g.:
>
> 'Statement' might work.
OK, updated patch attached. Is "statement" too vague here? SQL
statement? query?
--
Bruce Momjian <[email protected]> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ Everyone has their own god. +
diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
new file mode 100644
index cefd323..7d6e75b
*** a/doc/src/sgml/mvcc.sgml
--- b/doc/src/sgml/mvcc.sgml
***************
*** 41,52 ****
for developers to manage concurrent access to data. Internally,
data consistency is maintained by using a multiversion
model (Multiversion Concurrency Control, <acronym>MVCC</acronym>).
! This means that while querying a database each transaction sees
a snapshot of data (a <firstterm>database version</firstterm>)
as it was some
time ago, regardless of the current state of the underlying data.
! This protects the transaction from viewing inconsistent data that
! could be caused by (other) concurrent transaction updates on the same
data rows, providing <firstterm>transaction isolation</firstterm>
for each database session. <acronym>MVCC</acronym>, by eschewing
the locking methodologies of traditional database systems,
--- 41,52 ----
for developers to manage concurrent access to data. Internally,
data consistency is maintained by using a multiversion
model (Multiversion Concurrency Control, <acronym>MVCC</acronym>).
! This means that while querying a database each statement sees
a snapshot of data (a <firstterm>database version</firstterm>)
as it was some
time ago, regardless of the current state of the underlying data.
! This prevents statements from viewing inconsistent data produced
! by concurrent transactions performing updates on the same
data rows, providing <firstterm>transaction isolation</firstterm>
for each database session. <acronym>MVCC</acronym>, by eschewing
the locking methodologies of traditional database systems,
--
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