Query execute() API goes for inifinite wait (Hang)

Question

Hi
I am using BDB XML 2.4 in Fedora core-4. when I execute xquery update operation followed by FLWOR get query, the execute() API goes for infinite wait. We have tried setting NOWAIT flags to see if it waits for lock, but the program is in INFINITE wait (hang) state.
Below is the sample code and query I have used.
#include <dbxml/DbXml.hpp>
using namespace DbXml;
int
main(int argc, char **argv)
     std::string containerName = "myContainer.dbxml";
     std::string docFilename = "./NECB1.xml"; // the filename
     std::string queryString1 = "declare namespace SWI='SWI'; <getBulkResult> { let $i :=collection()//SWI:wmanIfBsOfdmaDownlinkChannelTable return ($i)} </getBulkResult>";
std::string queryString = "replace node collection()//SWI:wmanIfBsOfdmaDownlinkChannelTable/SWI:wmanIfBsOfdmaDownlinkChannelEntry[@ifIndex='2']/SWI:wmanIfBsOfdmaDownlinkCenterFreq with <SWI:wmanIfBsOfdmaDownlinkCenterFreq>3</SWI:wmanIfBsOfdmaDownlinkCenterFreq>";
     try {
          u_int32_t env_flags=DB_CREATE|DB_INIT_LOCK|DB_INIT_LOG|DB_INIT_MPOOL|DB_AUTO_COMMIT|DB_RECOVER|DB_INIT_TXN;
          DbEnv *clEnv = new DbEnv(0);
clEnv->open("/tmp",env_flags,0);
          XmlManager mgr;
          if (mgr.existsContainer(containerName))
               mgr.removeContainer(containerName);
          // Now it is safe to create the container
          XmlContainer cont = mgr.createContainer(containerName);
          u_int32_t cf =1000; //time out value in micro seconds
          clEnv->set_timeout(cf,DB_SET_LOCK_TIMEOUT);
          // All Container modification operations need XmlUpdateContext
          XmlUpdateContext uc = mgr.createUpdateContext();
          // Create the file input stream
XmlInputStream *myStream = mgr.createLocalFileInputStream(docFilename);
// Put the document in the container
cont.putDocument(docFilename, myStream, uc, 0); //TODO try without last parm(0)
          std::cout << "File loaded" << std::endl;
          // Querying requires an XmlQueryContext
          XmlQueryContext qc = mgr.createQueryContext();
          qc.setDefaultCollection(containerName);
          qc.setNamespace("SWI","SWI");
          std::cout << "update query " << std::endl;     
          XmlQueryExpression expr = mgr.prepare(queryString, qc);
          XmlResults res = expr.execute(qc);     //modify
          std::cout << "get query " << std::endl;     
          XmlQueryExpression expr1 = mgr.prepare(queryString1, qc);
XmlResults res1 = expr1.execute(qc);     //getbulk
          std::cout << "The query modify, '" << expr.getQuery() << "' returned " <<
          res.size() << " result(s)" << std::endl;
          XmlValue value;
          std::cout << "Result 1: " << std::endl;
          while (res.next(value)) {
               std::cout << "\t" << value.asString() << std::endl;
          std::cout << "The query 2 bulk , '" << expr1.getQuery() << "' returned " <<
res1.size() << " result(s)" << std::endl;
          XmlValue value1;
std::cout << "Result 2: " << std::endl;
while (res1.next(value1)) {
std::cout << "\t" << value1.asString() << std::endl;
     } catch (XmlException &xe) {
          std::cout << "XmlException: " << xe.what() << std::endl;
     return 0;
Sample output:
===========
[root@localhost santhosh]# ./query
File loaded
update query
get query
^C
Please let me know what could be the issue. Do I need to set any transaction related flags? I hope it should through exception if any setting/query is wrong.
Thanks,
Santhosh

Answer 1

Hi Santhosh,
Because you aren't using explicit transactions, your update query is being auto-transacted, and the read-only query is running without a transaction. This is very bad, and is giving you a self-deadlock situation. You should use an explicit transaction for your queries.
John