crud: add readview support

Added readview support for select and pairs.

Closes #343

CHANGELOG.md

@@ -5,12 +5,17 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Added
+* Read view support for select and pairs(#343).
+
 ## [1.2.0] - 07-06-23
 
 ### Added
-* Add `noreturn` option for operations: 
-  `insert`, `insert_object`, `insert_many`, `insert_object_many`, 
-  `replace`, `replace_object`, `replace_many`, `insert_object_many`, 
+* Add `noreturn` option for operations:
+  `insert`, `insert_object`, `insert_many`, `insert_object_many`,
+  `replace`, `replace_object`, `replace_many`, `insert_object_many`,
   `upsert`, `upsert_object`, `upsert_many`, `upsert_object_many`,
   `update`, `delete` (#267).
 
@@ -39,16 +44,16 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ## [1.0.0] - 02-02-23
 
 ### Added
-* Add timeout condition for the validation of master presence in 
+* Add timeout condition for the validation of master presence in
   replicaset and for the master connection (#95).
 * Support Cartridge clusterwide configuration for `crud.cfg` (#332).
 
 ### Changed
 * **Breaking**: forbid using space id in `crud.len` (#255).
 
 ### Fixed
-* Add validation of the master presence in replicaset and the 
-  master connection to the `utils.get_space` method before 
+* Add validation of the master presence in replicaset and the
+  master connection to the `utils.get_space` method before
   receiving the space from the connection (#331).
 * Fix fiber cancel on schema reload timeout in `call_reload_schema` (PR #336).
 

README.md

@@ -37,6 +37,12 @@ It also provides the `crud-storage` and `crud-router` roles for
   - [Count](#count)
   - [Call options for crud methods](#call-options-for-crud-methods)
   - [Statistics](#statistics)
+  - [Read view](#read-view)
+    - [Creating a read view](#creating-a-read-view)
+    - [Closing a read view](#closing-a-read-view)
+    - [Read view select](#read-view-select)
+      - [Read view select conditions](#read-view-select-conditions)
+    - [Read view pairs](#read-view-pairs)
 - [Cartridge roles](#cartridge-roles)
   - [Usage](#usage)
 - [License](#license)
@@ -237,8 +243,8 @@ where:
   * `noreturn` (`?boolean`) - suppress successfully processed tuple
     (first return value is `nil`). `false` by default
   * `fetch_latest_metadata` (`?boolean`) - guarantees the
-    up-to-date metadata (space format) in first return value, otherwise 
-    it may not take into account the latest migration of the data format. 
+    up-to-date metadata (space format) in first return value, otherwise
+    it may not take into account the latest migration of the data format.
     Performance overhead is up to 15%. `false` by default
 
 Returns metadata and array contains one inserted row, error.
@@ -308,8 +314,8 @@ where:
   * `noreturn` (`?boolean`) - suppress successfully processed tuples
     (first return value is `nil`). `false` by default
   * `fetch_latest_metadata` (`?boolean`) - guarantees the
-    up-to-date metadata (space format) in first return value, otherwise 
-    it may not take into account the latest migration of the data format. 
+    up-to-date metadata (space format) in first return value, otherwise
+    it may not take into account the latest migration of the data format.
     Performance overhead is up to 15%. `false` by default
 
 Returns metadata and array with inserted rows, array of errors.
@@ -450,8 +456,8 @@ where:
     vshard router instance. Set this parameter if your space is not
     a part of the default vshard cluster
   * `fetch_latest_metadata` (`?boolean`) - guarantees the
-    up-to-date metadata (space format) in first return value, otherwise 
-    it may not take into account the latest migration of the data format. 
+    up-to-date metadata (space format) in first return value, otherwise
+    it may not take into account the latest migration of the data format.
     Performance overhead is up to 15%. `false` by default
 
 Returns metadata and array contains one row, error.
@@ -493,8 +499,8 @@ where:
   * `noreturn` (`?boolean`) - suppress successfully processed tuple
     (first return value is `nil`). `false` by default
   * `fetch_latest_metadata` (`?boolean`) - guarantees the
-    up-to-date metadata (space format) in first return value, otherwise 
-    it may not take into account the latest migration of the data format. 
+    up-to-date metadata (space format) in first return value, otherwise
+    it may not take into account the latest migration of the data format.
     Performance overhead is up to 15%. `false` by default
 
 Returns metadata and array contains one updated row, error.
@@ -535,8 +541,8 @@ where:
   * `noreturn` (`?boolean`) - suppress successfully processed tuple
     (first return value is `nil`). `false` by default
   * `fetch_latest_metadata` (`?boolean`) - guarantees the
-    up-to-date metadata (space format) in first return value, otherwise 
-    it may not take into account the latest migration of the data format. 
+    up-to-date metadata (space format) in first return value, otherwise
+    it may not take into account the latest migration of the data format.
     Performance overhead is up to 15%. `false` by default
 
 Returns metadata and array contains one deleted row (empty for vinyl), error.
@@ -588,8 +594,8 @@ where:
   * `noreturn` (`?boolean`) - suppress successfully processed tuple
     (first return value is `nil`). `false` by default
   * `fetch_latest_metadata` (`?boolean`) - guarantees the
-    up-to-date metadata (space format) in first return value, otherwise 
-    it may not take into account the latest migration of the data format. 
+    up-to-date metadata (space format) in first return value, otherwise
+    it may not take into account the latest migration of the data format.
     Performance overhead is up to 15%. `false` by default
 
 Returns inserted or replaced rows and metadata or nil with error.
@@ -659,8 +665,8 @@ where:
   * `noreturn` (`?boolean`) - suppress successfully processed tuples
     (first return value is `nil`). `false` by default
   * `fetch_latest_metadata` (`?boolean`) - guarantees the
-    up-to-date metadata (space format) in first return value, otherwise 
-    it may not take into account the latest migration of the data format. 
+    up-to-date metadata (space format) in first return value, otherwise
+    it may not take into account the latest migration of the data format.
     Performance overhead is up to 15%. `false` by default
 
 Returns metadata and array with inserted/replaced rows, array of errors.
@@ -801,8 +807,8 @@ where:
   * `noreturn` (`?boolean`) - suppress successfully processed tuple
     (first return value is `nil`). `false` by default
   * `fetch_latest_metadata` (`?boolean`) - guarantees the
-    up-to-date metadata (space format) in first return value, otherwise 
-    it may not take into account the latest migration of the data format. 
+    up-to-date metadata (space format) in first return value, otherwise
+    it may not take into account the latest migration of the data format.
     Performance overhead is up to 15%. `false` by default
 
 Returns metadata and empty array of rows or nil, error.
@@ -868,8 +874,8 @@ where:
   * `noreturn` (`?boolean`) - suppress successfully processed tuples
     (first return value is `nil`). `false` by default
   * `fetch_latest_metadata` (`?boolean`) - guarantees the
-    up-to-date metadata (space format) in first return value, otherwise 
-    it may not take into account the latest migration of the data format. 
+    up-to-date metadata (space format) in first return value, otherwise
+    it may not take into account the latest migration of the data format.
     Performance overhead is up to 15%. `false` by default
 
 Returns metadata and array of errors.
@@ -1014,8 +1020,8 @@ where:
   * `yield_every` (`?number`) - number of tuples processed on storage to yield after,
     `yield_every` should be > 0, default value is 1000
   * `fetch_latest_metadata` (`?boolean`) - guarantees the
-    up-to-date metadata (space format) in first return value, otherwise 
-    it may not take into account the latest migration of the data format. 
+    up-to-date metadata (space format) in first return value, otherwise
+    it may not take into account the latest migration of the data format.
     Performance overhead is up to 15%. `false` by default
 
 
@@ -1541,6 +1547,198 @@ support preserving stats between role reload
 (see [tarantool/metrics#334](https://github.com/tarantool/metrics/issues/334)),
 thus this feature will be unsupported for `metrics` driver.
 
+### Read view
+
+A read view is an in-memory snapshot of the entire database that isn’t affected by future data modifications. Read views allow you to retrieve data using the `read_view_object:select()` and `read_view_object:pairs()` operations.
+
+Read views can be used to make complex analytical queries. This reduces the load on the main database and improves RPS for a single Tarantool instance.
+
+To improve memory consumption and performance, Tarantool creates read views using the copy-on-write technique. In this case, duplication of the entire data set is not required: Tarantool duplicates only blocks modified after a read view is created
+
+Read views have the following limitations:
+
+  * Only the memtx engine is supported.
+  * Read view can be used starting from Tarantool Enterprise v2.11.0.
+
+#### Creating a read view
+
+To create a read view, call the `crud.readview()` function.
+
+```lua
+local foo = crud.readview(opts)
+```
+
+where:
+
+* `opts`:
+  * `name` (`?string`) - name of the read view
+  * `timeout` (`?number`) - `vshard.call` timeout (in seconds)
+
+**Example:**
+
+```lua
+local foo = crud.readview({name: 'foo', timeout: 3})
+```
+
+#### Closing a read view
+
+When a read view is no longer needed, close it using the `read_view_object:close()` method because a read view may consume a substantial amount of memory.
+
+```lua
+local foo = foo.readview()
+foo:close(opts)
+```
+
+where:
+
+* `opts`:
+  * `timeout` (`?number`) - `vshard.call` timeout (in seconds)
+
+Otherwise, a read view is closed implicitly when the read view object is collected by the Lua garbage collector.
+
+**Example:**
+
+```lua
+local foo = crud.readview()
+foo:close({timeout = 3})
+```
+
+#### Read view select
+
+`read_view_object:select()` supports multi-conditional selects, treating a cluster as a single space, same as `crud.select`.
+
+```lua
+local foo = crud.readview()
+local objects, err = foo:select(space_name, conditions, opts)
+foo:close()
+```
+
+where:
+
+* `space_name` (`string`) - name of the space
+* `conditions` (`?table`) - array of [select conditions](#select-conditions)
+* `opts`:
+  * `first` (`?number`) - the maximum count of the objects to return.
+     If negative value is specified, the objects behind `after` are returned
+     (`after` option is required in this case). [See pagination examples](doc/select.md#pagination).
+  * `after` (`?table`) - tuple after which objects should be selected
+  * `batch_size` (`?number`) - number of tuples to process per one request to storage
+  * `bucket_id` (`?number|cdata`) - bucket ID
+  * `force_map_call` (`?boolean`) - if `true`
+     then the map call is performed without any optimizations even
+     if full primary key equal condition is specified
+  * `timeout` (`?number`) - `vshard.call` timeout (in seconds)
+  * `fields` (`?table`) - field names for getting only a subset of fields
+  * `fullscan` (`?boolean`) - if `true` then a critical log entry will be skipped
+    on potentially long `select`, see [avoiding full scan](doc/select.md#avoiding-full-scan).
+  * `vshard_router` (`?string|table`) - Cartridge vshard group name or
+    vshard router instance. Set this parameter if your space is not
+    a part of the default vshard cluster
+  * `yield_every` (`?number`) - number of tuples processed on storage to yield after,
+    `yield_every` should be > 0, default value is 1000
+  * `fetch_latest_metadata` (`?boolean`) - guarantees the
+    up-to-date metadata (space format) in first return value, otherwise
+    it may not take into account the latest migration of the data format.
+    Performance overhead is up to 15%. `false` by default
+
+
+Returns metadata and array of rows, error.
+
+**Example:**
+
+```lua
+local foo = crud.readview()
+foo:select('customers', nil, {batch_size=1, fullscan=true})
+---
+- metadata: [{'name': 'id', 'type': 'unsigned'}, {'name': 'bucket_id', 'type': 'unsigned'},
+    {'name': 'name', 'type': 'string'}, {'name': 'age', 'type': 'number'}]
+  rows:
+  - [1, 477, 'Elizabeth', 12]
+  - [2, 401, 'Mary', 46]
+  - [3, 2804, 'David', 33]
+  - [4, 1161, 'William', 81]
+  - [5, 1172, 'Jack', 35]
+  - [6, 1064, 'William', 25]
+  - [7, 693, 'Elizabeth', 18]
+- null
+...
+crud.insert('customers', {8, box.NULL, 'Elizabeth', 23})
+---
+- rows:
+  - [8, 185, 'Elizabeth', 23]
+  metadata: [{'name': 'id', 'type': 'unsigned'}, {'name': 'bucket_id', 'type': 'unsigned'},
+    {'name': 'name', 'type': 'string'}, {'name': 'age', 'type': 'number'}]
+- null
+...
+foo:select('customers', nil, {batch_size=1, fullscan=true})
+---
+- metadata: [{'name': 'id', 'type': 'unsigned'}, {'name': 'bucket_id', 'type': 'unsigned'},
+    {'name': 'name', 'type': 'string'}, {'name': 'age', 'type': 'number'}]
+  rows:
+  - [1, 477, 'Elizabeth', 12]
+  - [2, 401, 'Mary', 46]
+  - [3, 2804, 'David', 33]
+  - [4, 1161, 'William', 81]
+  - [5, 1172, 'Jack', 35]
+  - [6, 1064, 'William', 25]
+  - [7, 693, 'Elizabeth', 18]
+- null
+...
+foo.close()
+```
+
+##### Read view select conditions
+
+Select conditions for `read_view_object:select()` are the same as [select conditions](#select-conditions) for `crud.select`.
+
+**Example:**
+
+```lua
+foo = crud.readview()
+foo:select('customers', {{'<=', 'age', 35}}, {first = 10})
+---
+- metadata:
+  - {'name': 'id', 'type': 'unsigned'}
+  - {'name': 'bucket_id', 'type': 'unsigned'}
+  - {'name': 'name', 'type': 'string'}
+  - {'name': 'age', 'type': 'number'}
+  rows:
+  - [5, 1172, 'Jack', 35]
+  - [3, 2804, 'David', 33]
+  - [6, 1064, 'William', 25]
+  - [7, 693, 'Elizabeth', 18]
+  - [1, 477, 'Elizabeth', 12]
+...
+foo.close()
+```
+
+#### Read view pairs
+
+You can iterate across a distributed space using the `read_view_object:pairs()` method.
+Its arguments are the same as [`crud.readview.select`](#read-view-select) arguments except
+`fullscan` (it does not exist because `crud.pairs` does not generate a critical
+log entry on potentially long requests) and negative `first` values aren't
+allowed.
+User could pass use_tomap flag (false by default) to iterate over flat tuples or objects.
+
+**Example:**
+
+```lua
+foo = crud.readview()
+local tuples = {}
+for _, tuple in foo:pairs('customers', {{'<=', 'age', 35}}, {use_tomap = false}) do
+    -- {5, 1172, 'Jack', 35}
+    table.insert(tuples, tuple)
+end
+
+local objects = {}
+for _, object in foo:pairs('customers', {{'<=', 'age', 35}}, {use_tomap = true}) do
+    -- {id = 5, name = 'Jack', bucket_id = 1172, age = 35}
+    table.insert(objects, object)
+end
+foo:close()
+```
+
 ## Cartridge roles
 
 `cartridge.roles.crud-storage` is a Tarantool Cartridge role that depends on the

crud.lua

@@ -20,6 +20,7 @@ local borders = require('crud.borders')
 local sharding_metadata = require('crud.common.sharding.sharding_metadata')
 local utils = require('crud.common.utils')
 local stats = require('crud.stats')
+local readview = require('crud.readview')
 
 local crud = {}
 
@@ -147,6 +148,10 @@ crud.reset_stats = stats.reset
 -- @function storage_info
 crud.storage_info = utils.storage_info
 
+-- @refer readview.new
+-- @function readview
+crud.readview = readview.new
+
 --- Initializes crud on node
 --
 -- Exports all functions that are used for calls
@@ -174,6 +179,7 @@ function crud.init_storage()
     count.init()
     borders.init()
     sharding_metadata.init()
+    readview.init()
 
     _G._crud.storage_info_on_storage = utils.storage_info_on_storage
 end