Add docs for hdfs and fix some review comments

dbms/src/Common/parseGlobs.cpp

@@ -2,12 +2,13 @@
 #include <re2/re2.h>
 #include <re2/stringpiece.h>
 #include <algorithm>
+#include <sstream>
 
 namespace DB
 {
 /* Transforms string from grep-wildcard-syntax ("{N..M}", "{a,b,c}" as in remote table function and "*", "?") to perl-regexp for using re2 library fo matching
  * with such steps:
- * 1) search intervals and enums in {}, replace them by regexp with pipe (expr1|expr2|expr3),
+ * 1) search intervals like {0..9} and enums like {abc,xyz,qwe} in {}, replace them by regexp with pipe (expr1|expr2|expr3),
  * 2) search and replace "*" and "?".
  * Before each search need to escape symbols that we would not search.
  *
@@ -15,63 +16,60 @@ namespace DB
  */
 std::string makeRegexpPatternFromGlobs(const std::string & initial_str_with_globs)
 {
-    std::string escaped_with_globs;
-    escaped_with_globs.reserve(initial_str_with_globs.size());
+    std::ostringstream oss;
     /// Escaping only characters that not used in glob syntax
     for (const auto & letter : initial_str_with_globs)
     {
         if ((letter == '[') || (letter == ']') || (letter == '|') || (letter == '+') || (letter == '-') || (letter == '(') || (letter == ')'))
-            escaped_with_globs.push_back('\\');
-        escaped_with_globs.push_back(letter);
+            oss << '\\';
+        oss << letter;
     }
-
-    re2::RE2 enum_or_range(R"({([\d]+\.\.[\d]+|[^{}*,]+,[^{}*]*[^{}*,])})");    /// regexp for {expr1,expr2,expr3} or {M..N}, where M and N - non-negative integers, expr's should be without {}*,
+    std::string escaped_with_globs = oss.str();
+    oss.str("");
+    static const re2::RE2 enum_or_range(R"({([\d]+\.\.[\d]+|[^{}*,]+,[^{}*]*[^{}*,])})");    /// regexp for {expr1,expr2,expr3} or {M..N}, where M and N - non-negative integers, expr's should be without {}*,
     re2::StringPiece input(escaped_with_globs);
-    re2::StringPiece matched(escaped_with_globs);
+    re2::StringPiece matched;
     size_t current_index = 0;
-    std::string almost_regexp;
-    almost_regexp.reserve(escaped_with_globs.size());
     while (RE2::FindAndConsume(&input, enum_or_range, &matched))
     {
         std::string buffer = matched.ToString();
-        almost_regexp.append(escaped_with_globs.substr(current_index, matched.data() - escaped_with_globs.data() - current_index - 1));
+        oss << escaped_with_globs.substr(current_index, matched.data() - escaped_with_globs.data() - current_index - 1) << '(';
 
         if (buffer.find(',') == std::string::npos)
         {
-            size_t first_point = buffer.find('.');
-            std::string first_number = buffer.substr(0, first_point);
-            std::string second_number = buffer.substr(first_point + 2, buffer.size() - first_point - 2);
-            size_t range_begin = std::stoull(first_number);
-            size_t range_end = std::stoull(second_number);
-            buffer = std::to_string(range_begin);
+            size_t range_begin, range_end;
+            char point;
+            std::istringstream iss(buffer);
+            iss >> range_begin >> point >> point >> range_end;
+            oss << range_begin;
             for (size_t i = range_begin + 1; i <= range_end; ++i)
             {
-                buffer += "|";
-                buffer += std::to_string(i);
+                oss << '|' << i;
             }
         }
         else
         {
             std::replace(buffer.begin(), buffer.end(), ',', '|');
+            oss << buffer;
         }
-        almost_regexp.append("(" + buffer + ")");
+        oss << ")";
         current_index = input.data() - escaped_with_globs.data();
     }
-    almost_regexp += escaped_with_globs.substr(current_index);
-    std::string result;
-    result.reserve(almost_regexp.size());
-    for (const auto & letter : almost_regexp)
+    oss << escaped_with_globs.substr(current_index);
+    std::string almost_res = oss.str();
+    oss.str("");
+    for (const auto & letter : almost_res)
     {
         if ((letter == '?') || (letter == '*'))
         {
-            result += "[^/]";   /// '?' is any symbol except '/'
+            oss << "[^/]";   /// '?' is any symbol except '/'
             if (letter == '?')
                 continue;
         }
         if ((letter == '.') || (letter == '{') || (letter == '}'))
-            result.push_back('\\');
-        result.push_back(letter);
+            oss << '\\';
+        oss << letter;
     }
-    return result;
+    return oss.str();
 }
 }

docs/en/operations/table_engines/file.md

@@ -27,7 +27,7 @@ When creating table using `File(Format)` it creates empty subdirectory in that f
 You may manually create this subfolder and file in server filesystem and then [ATTACH](../../query_language/misc.md) it to table information with matching name, so you can query data from that file.
 
 !!! warning
-    Be careful with this funcionality, because ClickHouse does not keep track of external changes to such files. The result of simultaneous writes via ClickHouse and outside of ClickHouse is undefined.
+    Be careful with this functionality, because ClickHouse does not keep track of external changes to such files. The result of simultaneous writes via ClickHouse and outside of ClickHouse is undefined.
 
 **Example:**
 
@@ -73,9 +73,9 @@ $ echo -e "1,2\n3,4" | clickhouse-local -q "CREATE TABLE table (a Int64, b Int64
 
 - Multiple `SELECT` queries can be performed concurrently, but `INSERT` queries will wait each other.
 - Not supported:
-  - `ALTER`
-  - `SELECT ... SAMPLE`
-  - Indices
-  - Replication
+    - `ALTER`
+    - `SELECT ... SAMPLE`
+    - Indices
+    - Replication
 
 [Original article](https://clickhouse.yandex/docs/en/operations/table_engines/file/) <!--hide-->

docs/en/operations/table_engines/hdfs.md

+# HDFS {#table_engines-hdfs}
+
+Manages data on HDFS. This engine is similar
+to the [File](file.md) and [URL](url.md) engine.
+
+## Usage
+
+```
+ENGINE = HDFS(URI, format)
+```
+
+The `format` parameter specifies one of the available file formats. To perform
+`SELECT` queries, the format must be supported for input, and to perform
+`INSERT` queries -- for output. The available formats are listed in the
+[Formats](../../interfaces/formats.md#formats) section.
+
+**Example:**
+
+**1.** Set up the `HDFS_engine_table` table:
+
+``` sql
+CREATE TABLE hdfs_engine_table (name String, value UInt32) ENGINE=HDFS('hdfs://hdfs1:9000/other_storage', 'TSV')
+```
+**2.** Query the data:
+
+``` sql
+SELECT * FROM hdfs_engine_table LIMIT 2
+```
+
+```
+┌─name─┬─value─┐
+│ one  │     1 │
+│ two  │     2 │
+└──────┴───────┘
+```
+
+## Details of Implementation
+
+- Reads and writes can be parallel
+- Not supported:
+    - `ALTER` and `SELECT...SAMPLE` operations.
+    - Indexes.
+    - Replication.
+
+[Original article](https://clickhouse.yandex/docs/en/operations/table_engines/hdfs/) <!--hide-->

docs/en/query_language/table_functions/file.md

@@ -11,7 +11,7 @@ file(path, format, structure)
 
 - `path` — The relative path to the file from [user_files_path](../../operations/server_settings/settings.md#server_settings-user_files_path).
 - `format` —  The [format](../../interfaces/formats.md#formats) of the file.
-- `structure` — Structure of the table. Format `'colunmn1_name column1_ype, column2_name column2_type, ...'`.
+- `structure` — Structure of the table. Format `'column1_name column1_type, column2_name column2_type, ...'`.
 
 **Returned value**
 

docs/en/query_language/table_functions/hdfs.md

+
+# hdfs
+
+Creates a table from a file in hdfs.
+
+```
+hdfs(URI, format, structure)
+```
+
+**Input parameters**
+
+- `URI` — The relative URI to the file in HDFS.
+- `format` —  The [format](../../interfaces/formats.md#formats) of the file.
+- `structure` — Structure of the table. Format `'column1_name column1_type, column2_name column2_type, ...'`.
+
+**Returned value**
+
+A table with the specified structure for reading or writing data in the specified file.
+
+**Example**
+
+Table from `hdfs://hdfs1:9000/test` and selection of the first two rows from it:
+
+```sql
+SELECT *
+FROM hdfs('hdfs://hdfs1:9000/test', 'TSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
+LIMIT 2
+```
+
+```
+┌─column1─┬─column2─┬─column3─┐
+│       1 │       2 │       3 │
+│       3 │       2 │       1 │
+└─────────┴─────────┴─────────┘
+```
+
+[Original article](https://clickhouse.yandex/docs/en/query_language/table_functions/hdfs/) <!--hide-->

docs/ru/operations/table_engines/hdfs.md

+# HDFS {#table_engines-hdfs}
+
+Управляет данными в HDFS. Данный движок похож на движок [File](file.md) и на движок [URL](url.md).
+
+## Использование движка
+
+```
+ENGINE = HDFS(URI, format)
+```
+
+Параметр `format` должен быть таким, который ClickHouse может использовать и в запросах `INSERT`, и в запросах `SELECT`. Полный список поддерживаемых форматов смотрите в разделе [Форматы](../../interfaces/formats.md#formats).
+
+**Пример:**
+
+**1.** Создадим на сервере таблицу `hdfs_engine_table`:
+
+``` sql
+CREATE TABLE hdfs_engine_table (name String, value UInt32) ENGINE=HDFS('hdfs://hdfs1:9000/other_storage', 'TSV')
+```
+
+**2.** Запросим данные:
+
+``` sql
+SELECT * FROM hdfs_engine_table LIMIT 2
+```
+
+```
+┌─name─┬─value─┐
+│ one  │     1 │
+│ two  │     2 │
+└──────┴───────┘
+```
+
+## Детали реализации
+
+- Поддерживается многопоточное чтение и запись.
+- Не поддерживается:
+    - использование операций `ALTER` и `SELECT...SAMPLE`;
+    - индексы;
+    - репликация.
+
+[Оригинальная статья](https://clickhouse.yandex/docs/ru/operations/table_engines/hdfs/) <!--hide-->

docs/ru/query_language/table_functions/hdfs.md

+
+# hdfs
+
+Создаёт таблицу из файла.
+
+```
+hdfs(URI, format, structure)
+```
+
+**Входные параметры**
+
+- `URI` — URI до файла в HDFS.
+- `format` — [формат](../../interfaces/formats.md#formats) файла.
+- `structure` — структура таблицы. Формат `'column1_name column1_type, column2_name column2_type, ...'`.
+
+**Возвращаемое значение**
+
+Таблица с указанной структурой, предназначенная для чтения или записи данных в указанном файле.
+
+**Пример**
+
+Таблица из `hdfs://hdfs1:9000/test` и выборка первых двух строк из неё:
+
+``` sql
+SELECT *
+FROM hdfs('hdfs://hdfs1:9000/test', 'TSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
+LIMIT 2
+```
+```
+┌─column1─┬─column2─┬─column3─┐
+│       1 │       2 │       3 │
+│       3 │       2 │       1 │
+└─────────┴─────────┴─────────┘
+```
+
+[Оригинальная статья](https://clickhouse.yandex/docs/ru/query_language/table_functions/hdfs/) <!--hide-->