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| - %META:TOPICPARENT{name="VirtTipsAndTricksGuide"}%
---++Reading Virtuoso Transaction Logs
---++What?
A Stored Procedure that uses the in-built [[http://docs.openlinksw.com/virtuoso/fn_read_log.html][read_log()]] function to read the Transaction log of a Virtuoso Instance, in regards to Quad Store activity.
---++Why?
There are times when you application functionality benefits from being able to read Virtuoso Transaction logs. In particular, the database triggers on the <code>RDF_QUAD</code> table are not meant to be supported in Virtuoso 7+, thus reading transaction logs as indicated below is the recommended method for tracking changes to the <code>RDF_QUAD</code> table.
---++How?
To read the changes made to the <code>RDF_QUAD</code> table i.e RDF data, one can use the following Virtuoso Stored procedure that uses the in-built [[http://docs.openlinksw.com/virtuoso/fn_read_log.html][read_log()]]:
---+++Sample Scenario
1 Insert sample data so to change the rdf_quad index:
<verbatim>
SQL> SPARQL INSERT INTO <g> { <s> <p> <o> };
</verbatim>
1 Create the following example procedure:
<verbatim>
create procedure rlt (in f any, in inpos int := 0)
{
declare h, op, g, s, p, o any;
declare pos int;
result_names (op, g, s, p, o);
h := file_open (f, inpos);
declare r, rr any;
while ((rr := read_log (h, pos)) is not null)
{
declare rw, k any;
declare i int;
rw := null;
k := null;
for (i := 1; i < length (rr); i := i + 1)
{
r := rr[i];
if (r[0] = 13) -- key insert
{
rw := r[2];
op := 'I';
}
else if (r[0] in (1,8,9)) -- insert,soft,replacing
{
rw := r[1];
op := 'I';
}
else if (r[0] in (3,14)) -- delete
{
rw := r[1];
op := 'D';
}
if (rw is not null)
{
k := rw[0];
if (k = 273) -- RDF_QUAD, should check with SYS_KEYS
{
result (op, __ro2sq (rw[1]), __ro2sq (rw[2]), __ro2sq (rw[3]), __ro2sq (rw[4]));
}
}
}
}
result (pos + inpos, '', '', '', '');
}
;
</verbatim>
1 Call the procedure:
* In case of no changes to the <code><nowiki>RDF_QUAD</nowiki> Index</code> are done, it will return:
<verbatim>
SQL> rlt('tmp/Virtuoso.trx');
Query result:
op g s p o
ANY ANY ANY ANY ANY
8403
No. of rows in result: 1
</verbatim>
* In case of changes to the <code><nowiki>RDF_QUAD</nowiki> Index</code> are done ( example with the short INSERT we did above), it will return for example:
<verbatim>
SQL> rlt('tmp/Virtuoso.trx');
Query result:
op g s p o
ANY ANY ANY ANY ANY
I g s p o
71446
No. of rows in result: 2
</verbatim>
To read the transaction log in general, one should use the Virtuoso [[http://docs.openlinksw.com/virtuoso/fn_read_log.html][read_log()]] function.
---++Related
* [[http://docs.openlinksw.com/virtuoso/vsp1.html#longhttptrans][Long HTTP Transactions.]]
* [[http://docs.openlinksw.com/virtuoso/clusteroperation.html#clusteroperationtransc][Cluster Operations transactions.]]
* [[http://docs.openlinksw.com/virtuoso/fn_log_text.html][Insert a SQL statement into the roll forward log.]]
* [[http://docs.openlinksw.com/virtuoso/fn_log_enable.html][Enable logs.]]
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