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docs: clarify MVCC introduction to allow for per-statement snapshots

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Bruce Momjian 2013-11-13 10:14:05 -05:00
parent fe67d25233
commit cd8115e009
1 changed files with 3 additions and 3 deletions
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doc/src/sgml/mvcc.sgml
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@ -41,12 +41,12 @@
for developers to manage concurrent access to data. Internally, for developers to manage concurrent access to data. Internally,
data consistency is maintained by using a multiversion data consistency is maintained by using a multiversion
model (Multiversion Concurrency Control, <acronym>MVCC</acronym>). model (Multiversion Concurrency Control, <acronym>MVCC</acronym>).
This means that while querying a database each transaction sees This means that each SQL statement sees
a snapshot of data (a <firstterm>database version</firstterm>) a snapshot of data (a <firstterm>database version</firstterm>)
as it was some as it was some
time ago, regardless of the current state of the underlying data. time ago, regardless of the current state of the underlying data.
This protects the transaction from viewing inconsistent data that This prevents statements from viewing inconsistent data produced
could be caused by (other) concurrent transaction updates on the same by concurrent transactions performing updates on the same
data rows, providing <firstterm>transaction isolation</firstterm> data rows, providing <firstterm>transaction isolation</firstterm>
for each database session. <acronym>MVCC</acronym>, by eschewing for each database session. <acronym>MVCC</acronym>, by eschewing
the locking methodologies of traditional database systems, the locking methodologies of traditional database systems,