%META:TOPICPARENT{name="VirtuosoWikiWebIndex"}%

= Changing the Default Transaction Isolation Level for a Virtuoso Server Instance =

Note that changing this default may have significant impact on performance.  For most mixed-use deployments, the unset default of {{{READ COMMITTED}}} should be left unchanged.

Transaction isolation may always be changed for individual [[http://docs.openlinksw.com/virtuoso/isolation/|SQL sessions]].

SPARQL does not support transaction isolation adjustments at the session level, so users focused on RDF interaction may need to adjust this to, for instance, {{{REPEATABLE READ}}} or other setting in the table below.

# Log in to the machine that hosts your Virtuoso Universal Server.
# Open the relevant {{{virtuoso.ini}}} file in a text editor.
# Locate the {{{[Parameters]}}} section of the file. For example:
{{{
[Parameters]
ServerPort               = 1111
DisableUnixSocket        = 1
;SSLServerPort           = 2111
...
DefaultIsolation         = 4
...
}}}
# Locate the {{{DefaultIsolation}}} parameter.
# Pass the numeric value for the desired isolation level
|  *Numeric Value*  |  *Transaction Isolation Level*  |
|  <i>unset</i> |  as if set to 2, <code>READ COMMITTED</code>  |
|  1  |  <code>READ UNCOMMITTED</code>  |
|  2  |  <code>READ COMMITTED</code>  |
|  4  |  <code>REPEATABLE READ</code>  |
|  8  |  <code>SERIALIZABLE</code>  |
For example:
{{{
DefaultIsolation = 1   ; READ UNCOMMITTED
}}}
# Save your changes and exit the file.
# Restart your Virtuoso server.

== Related ==

* [[http://docs.openlinksw.com/virtuoso/isolation/|Virtuso SQL Transaction Isolation]]
* [[http://docs.openlinksw.com/virtuoso/lockescalation/|Virtuoso Lock Escalation]]
* [[http://docs.openlinksw.com/virtuoso/lockescalation/|Virtuoso Locking]]
* [[https://docs.microsoft.com/en-us/sql/odbc/reference/develop-app/transaction-isolation-levels?view=sql-server-ver15|ODBC Transaction Isolation Levels]]