diff --git a/src/prefiltering/ungappedprefilter.cpp b/src/prefiltering/ungappedprefilter.cpp
index ded594304..460ffebfc 100644
--- a/src/prefiltering/ungappedprefilter.cpp
+++ b/src/prefiltering/ungappedprefilter.cpp
@@ -62,6 +62,7 @@ int doRescorealldiagonal(Parameters &par, DBReader<unsigned int> &qdbr, DBWriter
 
 
     Debug::Progress progress(dbSize);
+    std::vector<hit_t> shortResults;
 
 #pragma omp parallel
     {
@@ -70,8 +71,7 @@ int doRescorealldiagonal(Parameters &par, DBReader<unsigned int> &qdbr, DBWriter
         thread_idx = (unsigned int) omp_get_thread_num();
 #endif
         char buffer[1024+32768];
-        std::vector<hit_t> shortResults;
-        shortResults.reserve(std::max(static_cast<size_t >(1), tdbr->getSize()/5));
+        std::vector<hit_t> threadShortResults;
         Sequence qSeq(par.maxSeqLen, querySeqType, subMat, 0, false, par.compBiasCorrection);
         Sequence tSeq(par.maxSeqLen, targetSeqType, subMat, 0, false, par.compBiasCorrection);
         SmithWaterman aligner(par.maxSeqLen, subMat->alphabetSize,
@@ -79,8 +79,8 @@ int doRescorealldiagonal(Parameters &par, DBReader<unsigned int> &qdbr, DBWriter
 
         std::string resultBuffer;
         resultBuffer.reserve(262144);
-#pragma omp for schedule(dynamic, 1)
         for (size_t id = dbStart; id < (dbStart+dbSize); id++) {
+#pragma omp master
             progress.updateProgress();
             char *querySeqData = qdbr.getData(id, thread_idx);
             size_t queryKey = qdbr.getDbKey(id);
@@ -93,7 +93,7 @@ int doRescorealldiagonal(Parameters &par, DBReader<unsigned int> &qdbr, DBWriter
             }else{
                 aligner.ssw_init(&qSeq, tinySubMat, subMat);
             }
-
+#pragma omp for schedule(dynamic, 1) nowait
             for (size_t tId = 0; tId < tdbr->getSize(); tId++) {
                 unsigned int targetKey = tdbr->getDbKey(tId);
                 const bool isIdentity = (queryKey == targetKey && (par.includeIdentity || sameDB))? true : false;
@@ -109,7 +109,11 @@ int doRescorealldiagonal(Parameters &par, DBReader<unsigned int> &qdbr, DBWriter
 
                 int score = aligner.ungapped_alignment(tSeq.numSequence, tSeq.L);
                 bool hasDiagScore = (score > par.minDiagScoreThr);
-                double evalue = evaluer->computeEvalue(score, qSeq.L);
+                double evalue = 0.0;
+                // check if evalThr != inf
+                if (par.evalThr < std::numeric_limits<double>::max()) {
+                    evalue = evaluer->computeEvalue(score, qSeq.L);
+                }
                 bool hasEvalue = (evalue <= par.evalThr);
                 // --filter-hits
                 if (isIdentity || (hasDiagScore && hasEvalue)) {
@@ -117,20 +121,28 @@ int doRescorealldiagonal(Parameters &par, DBReader<unsigned int> &qdbr, DBWriter
                     hit.seqId = targetKey;
                     hit.prefScore = score;
                     hit.diagonal = 0;
-                    shortResults.emplace_back(hit);
+                    threadShortResults.emplace_back(hit);
                 }
             }
-
-            SORT_SERIAL(shortResults.begin(), shortResults.end(), hit_t::compareHitsByScoreAndId);
-            size_t maxSeqs = std::min(par.maxResListLen, shortResults.size());
-            for (size_t i = 0; i < maxSeqs; ++i) {
-                size_t len = QueryMatcher::prefilterHitToBuffer(buffer, shortResults[i]);
-                resultBuffer.append(buffer, len);
+#pragma omp critical
+            {
+                shortResults.insert(shortResults.end(), threadShortResults.begin(), threadShortResults.end());
+                threadShortResults.clear();
             }
+#pragma omp barrier
+#pragma omp master
+            {
+                SORT_PARALLEL(shortResults.begin(), shortResults.end(), hit_t::compareHitsByScoreAndId);
+                size_t maxSeqs = std::min(par.maxResListLen, shortResults.size());
+                for (size_t i = 0; i < maxSeqs; ++i) {
+                    size_t len = QueryMatcher::prefilterHitToBuffer(buffer, shortResults[i]);
+                    resultBuffer.append(buffer, len);
+                }
 
-            resultWriter.writeData(resultBuffer.c_str(), resultBuffer.length(), queryKey, thread_idx);
-            resultBuffer.clear();
-            shortResults.clear();
+                resultWriter.writeData(resultBuffer.c_str(), resultBuffer.length(), queryKey, 0);
+                resultBuffer.clear();
+                shortResults.clear();
+            }
         }
     }
 
@@ -163,7 +175,7 @@ int ungappedprefilter(int argc, const char **argv, const Command &command) {
 
     qdbr.decomposeDomainByAminoAcid(MMseqsMPI::rank, MMseqsMPI::numProc, &dbFrom, &dbSize);
     std::pair<std::string, std::string> tmpOutput = Util::createTmpFileNames(par.db3, par.db3Index, MMseqsMPI::rank);
-    DBWriter resultWriter(tmpOutput.first.c_str(), tmpOutput.second.c_str(), par.threads,  par.compressed, Parameters::DBTYPE_PREFILTER_RES);
+    DBWriter resultWriter(tmpOutput.first.c_str(), tmpOutput.second.c_str(), 1  par.compressed, Parameters::DBTYPE_PREFILTER_RES);
     resultWriter.open();
     int status = doRescorealldiagonal(par, qdbr, resultWriter, dbFrom, dbSize);
     resultWriter.close();
@@ -178,7 +190,7 @@ int ungappedprefilter(int argc, const char **argv, const Command &command) {
         DBWriter::mergeResults(par.db3, par.db3Index, splitFiles);
     }
 #else
-    DBWriter resultWriter(par.db3.c_str(), par.db3Index.c_str(), par.threads, par.compressed, Parameters::DBTYPE_PREFILTER_RES);
+    DBWriter resultWriter(par.db3.c_str(), par.db3Index.c_str(), 1, par.compressed, Parameters::DBTYPE_PREFILTER_RES);
     resultWriter.open();
     int status = doRescorealldiagonal(par, qdbr, resultWriter, 0, qdbr.getSize());
     resultWriter.close();