Hi,
I would like to have a confirmation about the handling of side effects
(that is, everything related to MVCC) in the context of try/catch. I
always thought that "whatever was executed in a try clause" before an error
is raised was going to be kept if the error is caught.
I know there is an incertainty WRT the order of execution, but still, I
thought some DB modifications called in the try clause could be kept in
case the error is caught.
Here is an example that tries to replicate the problem, using a recursive
function to beat the optimiser (full code at the end of this email):
local:side-effect('before'),
try {
local:recurse(('one', 'two'))
}
catch * {
'Caught error in main module'
},
local:side-effect('after')
In the above example, the result is that both /before.xml and /after.xml
are created, but not /one.xml (the creation is called during the first
iteration of the recursive function though).
All the tests I made have the same result: all DB modifications in the try
clause are discarded in case an error is raised (regardless it is caught or
not).
I could not find a definitive answer in the doc. Is this guaranteed?
Full example:
xquery version "3.0";
declare namespace xdmp = "http://marklogic.com/xdmp";;
declare function local:side-effect($name as xs:string)
{
xdmp:document-insert(
'/' || $name || '.xml',
<hello>{ $name }</hello>)
};
declare function local:recurse($names as xs:string)
{
if ( fn:count($names) eq 1 ) then (
fn:error((), 'Climb the stack...')
)
else (
local:side-effect(fn:head($names)),
local:recurse(fn:tail($names))
)
};
local:side-effect('before'),
try {
local:recurse(('one', 'two'))
}
catch * {
'Caught error in main module'
},
local:side-effect('after')
Regards,
--
Florent Georges
H2O Consulting
http://h2o.consulting/
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