fix empty segment cannot merge after gc (#4523)

close #4511

dbms/src/Debug/dbgFuncMisc.cpp

@@ -8,28 +8,73 @@
 
 namespace DB
 {
+inline size_t getThreadIdForLog(const String & line)
+{
+    auto sub_line = line.substr(line.find("thread_id="));
+    std::regex rx(R"((0|[1-9][0-9]*))");
+    std::smatch m;
+    if (regex_search(sub_line, m, rx))
+        return std::stoi(m[1]);
+    else
+        return 0;
+}
+
+// Usage example:
+// The first argument is the key you want to search.
+// For example, we want to search the key 'RSFilter exclude rate' in log file, and get the value following it.
+// So we can use it as the first argument.
+// But many kind of thread can print this keyword,
+// so we can use the second argument to specify a keyword that may just be printed by a specific kind of thread.
+// Here we use 'Rough set filter' to specify we just want to search read thread.
+// And the complete command is the following:
+//   DBGInvoke search_log_for_key('RSFilter exclude rate', 'Rough set filter')
+// TODO: this is still a too hack way to do test, but cannot think a better way now.
 void dbgFuncSearchLogForKey(Context & context, const ASTs & args, DBGInvoker::Printer output)
 {
-    if (args.size() < 1)
-        throw Exception("Args not matched, should be: key", ErrorCodes::BAD_ARGUMENTS);
+    if (args.size() < 2)
+        throw Exception("Args not matched, should be: key, thread_hint", ErrorCodes::BAD_ARGUMENTS);
 
     String key = safeGet<String>(typeid_cast<const ASTLiteral &>(*args[0]).value);
+    // the candidate line must be printed by a thread which also print a line contains `thread_hint`
+    String thread_hint = safeGet<String>(typeid_cast<const ASTLiteral &>(*args[1]).value);
     auto log_path = context.getConfigRef().getString("logger.log");
 
     std::ifstream file(log_path);
-    std::vector<String> line_candidates;
-    String line;
-    while (std::getline(file, line))
+    // get the lines containing `thread_hint` and `key`
+    std::vector<String> thread_hint_line_candidates;
+    std::vector<String> key_line_candidates;
     {
-        if ((line.find(key) != String::npos) && (line.find("DBGInvoke") == String::npos))
-            line_candidates.emplace_back(line);
+        String line;
+        while (std::getline(file, line))
+        {
+            if ((line.find(thread_hint) != String::npos) && (line.find("DBGInvoke") == String::npos))
+                thread_hint_line_candidates.emplace_back(line);
+            else if ((line.find(key) != String::npos) && (line.find("DBGInvoke") == String::npos))
+                key_line_candidates.emplace_back(line);
+        }
     }
-    if (line_candidates.empty())
+    // get target thread id
+    if (thread_hint_line_candidates.empty() || key_line_candidates.empty())
     {
         output("Invalid");
         return;
     }
-    auto & target_line = line_candidates.back();
+    size_t target_thread_id = getThreadIdForLog(thread_hint_line_candidates.back());
+    if (target_thread_id == 0)
+    {
+        output("Invalid");
+        return;
+    }
+    String target_line;
+    for (auto iter = key_line_candidates.rbegin(); iter != key_line_candidates.rend(); iter++)
+    {
+        if (getThreadIdForLog(*iter) == target_thread_id)
+        {
+            target_line = *iter;
+            break;
+        }
+    }
+    // try parse the first number following the key
     auto sub_line = target_line.substr(target_line.find(key));
     std::regex rx(R"([+-]?([0-9]+([.][0-9]*)?|[.][0-9]+))");
     std::smatch m;

dbms/src/Storages/DeltaMerge/Delta/DeltaPackFile.cpp

@@ -22,7 +22,7 @@ void DeltaPackFile::calculateStat(const DMContext & context)
     auto hash_salt = context.hash_salt;
 
     auto pack_filter
-        = DMFilePackFilter::loadFrom(file, index_cache, hash_salt, {segment_range}, EMPTY_FILTER, {}, context.db_context.getFileProvider(), context.getReadLimiter());
+        = DMFilePackFilter::loadFrom(file, index_cache, hash_salt, /*set_cache_if_miss*/ false, {segment_range}, EMPTY_FILTER, {}, context.db_context.getFileProvider(), context.getReadLimiter());
 
     std::tie(valid_rows, valid_bytes) = pack_filter.validRowsAndBytes();
 }
@@ -56,7 +56,7 @@ DeltaPackPtr DeltaPackFile::deserializeMetadata(DMContext & context, //
 
     auto dmfile = DMFile::restore(context.db_context.getFileProvider(), file_id, file_ref_id, file_parent_path, DMFile::ReadMetaMode::all());
 
-    auto dp_file = new DeltaPackFile(dmfile, valid_rows, valid_bytes, segment_range);
+    auto * dp_file = new DeltaPackFile(dmfile, valid_rows, valid_bytes, segment_range);
     return std::shared_ptr<DeltaPackFile>(dp_file);
 }
 
@@ -132,7 +132,7 @@ size_t DPFileReader::readRowsOnce(MutableColumns & output_cols, //
                                   const RowKeyRange * range)
 {
     auto read_next_block = [&, this]() -> bool {
-        rows_before_cur_block += ((bool)cur_block) ? cur_block.rows() : 0;
+        rows_before_cur_block += (static_cast<bool>(cur_block)) ? cur_block.rows() : 0;
         cur_block_data.clear();
 
         cur_block = file_stream->read();