The query parsing probes are triggered before the original SQL statement is parsed and when the parsing of the statement and determination of the execution model required to process the statement has been completed:
query-parse-start(query) query-parse-done(status)
query-parse-start: Triggered just before the statement is parsed by the MySQL query parser. The single argument,query, is a string containing the full text of the original query.query-parse-done: Triggered when the parsing of the original statement has been completed. Thestatusis an integer describing the status of the operation. A0indicates that the query was successfully parsed. A1indicates that the parsing of the query failed.
For example, you could monitor the execution time for parsing a given query using the following D script:
#!/usr/sbin/dtrace -s
#pragma D option quiet
mysql*:::query-parse-start
{
self->parsestart = timestamp;
self->parsequery = copyinstr(arg0);
}
mysql*:::query-parse-done
/arg0 == 0/
{
printf("Parsing %s: %d microseconds\n", self->parsequery,((timestamp - self->parsestart)/1000));
}
mysql*:::query-parse-done
/arg0 != 0/
{
printf("Error parsing %s: %d microseconds\n", self->parsequery,((timestamp - self->parsestart)/1000));
}
In the above script a predicate is used on
query-parse-done so that different output is
generated based on the status value of the probe.
When running the script and monitoring the execution:
shell> ./query-parsing.d Error parsing select from t1 join (t2) on (t1.i = t2.i) order by t1.s,t1.i limit 10: 36 ms Parsing select * from t1 join (t2) on (t1.i = t2.i) order by t1.s,t1.i limit 10: 176 ms