mirrors/postgres
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Doc: Add references for SI and SSI.

Browse Source 
Our documentation failed to point out that REPEATABLE READ is really
snapshot isolation, which might be important to some users.  Point to
the standard reference paper for this complicated topic.

Likewise, add a reference to the VLDB paper about PostgreSQL SSI, for
technical information about our SSI implementation and how it compares
to S2PL.

While here, add a note about catalog access using a lower isolation
level, per recent user complaint.

Back-patch to all releases.

Reported-by: Kyle Kingsbury <aphyr@jepsen.io>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Peter Geoghegan <pg@bowt.ie>
Reviewed-by: Tatsuo Ishii <ishii@sraoss.co.jp>
Discussion: https://postgr.es/m/db7b729d-0226-d162-a126-8a8ab2dc4443%40jepsen.io
Discussion: https://postgr.es/m/16454-9408996bb1750faf%40postgresql.org
This commit is contained in:
Thomas Munro 2020-06-15 11:33:13 +12:00
parent da0a60c3d7
commit 648e56d398
2 changed files with 91 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

58
doc/src/sgml/biblio.sgml
View File

@ -222,6 +222,64 @@ ssimkovi@ag.or.at
<bibliodiv>
<title>Proceedings and Articles</title>
<biblioentry id="ports12">
<biblioset relation="article">
<title><ulink url="https://arxiv.org/pdf/1208.4179">Serializable Snapshot Isolation in PostgreSQL</ulink></title>
<authorgroup>
<author>
<firstname>D.</firstname>
<surname>Ports</surname>
</author>
<author>
<firstname>K.</firstname>
<surname>Grittner</surname>
</author>
</authorgroup>
</biblioset>
<confgroup>
<conftitle>VLDB Conference</conftitle>
<confdates>August 2012</confdates>
<address>Istanbul, Turkey</address>
</confgroup>
</biblioentry>
<biblioentry id="berenson95">
<biblioset relation="article">
<title><ulink url="https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/tr-95-51.pdf">A Critique of ANSI SQL Isolation Levels</ulink></title>
<authorgroup>
<author>
<firstname>H.</firstname>
<surname>Berenson</surname>
</author>
<author>
<firstname>P.</firstname>
<surname>Bernstein</surname>
</author>
<author>
<firstname>J.</firstname>
<surname>Gray</surname>
</author>
<author>
<firstname>J.</firstname>
<surname>Melton</surname>
</author>
<author>
<firstname>E.</firstname>
<surname>O'Neil</surname>
</author>
<author>
<firstname>P.</firstname>
<surname>O'Neil</surname>
</author>
</authorgroup>
</biblioset>
<confgroup>
<conftitle>ACM-SIGMOD Conference on Management of Data</conftitle>
<confdates>June 1995</confdates>
<address>San Jose, California</address>
</confgroup>
</biblioentry>
<biblioentry id="olson93">
<title>Partial indexing in POSTGRES: research project</title>
<authorgroup>

33
doc/src/sgml/mvcc.sgml
View File

@ -535,6 +535,20 @@ ERROR: could not serialize access due to concurrent update
of explicit locks to block conflicting transactions.
</para>
<para>
The Repeatable Read isolation level is implemented using a technique
known in academic database literature and in some other database products
as <firstterm>Snapshot Isolation</firstterm>. Differences in behavior
and performance may be observed when compared with systems that use a
traditional locking technique that reduces concurrency. Some other
systems may even offer Repeatable Read and Snapshot Isolation as distinct
isolation levels with different behavior. The permitted phenomena that
distinguish the two techniques were not formalized by database researchers
until after the SQL standard was developed, and are outside the scope of
this manual. For a full treatment, please see
<xref linkend="berenson95"/>.
</para>
<note>
<para>
Prior to <productname>PostgreSQL</productname> version 9.1, a request
@ -783,6 +797,15 @@ ERROR: could not serialize access due to read/write dependencies among transact
</listitem>
</itemizedlist>
</para>
<para>
The Serializable isolation level is implemented using a technique known
in academic database literature as Serializable Snapshot Isolation, which
builds on Snapshot Isolation by adding checks for serialization anomalies.
Some differences in behavior and performance may be observed when compared
with other systems that use a traditional locking technique. Please see
<xref linkend="ports12"/> for detailed information.
</para>
</sect2>
</sect1>
@ -1716,6 +1739,16 @@ SELECT pg_advisory_lock(q.id) FROM
see a transient state that is inconsistent with any serial execution
of the transactions on the master.
</para>
<para>
Internal access to the system catalogs is not done using the isolation
level of the current transaction. This means that newly created database
objects such as tables are visible to concurrent Repeatable Read and
Serializable transactions, even though the rows they contain are not. In
contrast, queries that explicitly examine the system catalogs don't see
rows representing concurrently created database objects, in the higher
isolation levels.
</para>
</sect1>
<sect1 id="locking-indexes">