MySQL-InnoDB

InnoDB–MySQL Storage Engine
Mayank Prasad
InnoDB Developer 
November 12, 2019
Copyright © 2019, Oracle and/or its affiliates. All rights reserved.

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2

About Me
Mayank Prasad
• M.tech Computer Science.
• Consulting Member Technical Staff at Oracle-MySQL.
• Part of MySQL Server Development team since 2011.
• Worked in MySQL-Performance Schema Development for 6 years.
• Joined InnoDB development team in 2017.
• Reach me :
• @manku (Twitter)

A brief intro
Latest Features
Performance & Scalability
Q&A
4
Agenda

A brief intro
Latest Features
Q&A
5
Agenda


[JDBC, ODBC, .NET, PHP, Python, C API, Perl]

Logs (bootstrap/error/slow query/binary/redo/undo), files (.ibd
files etc.)
[Java, .NET, PHP, Python, C, Perl]
Pluggable Storage Engine APIs Interface
Achieve Memory PFSMyISAM
Connection Pool Authentication/Authorization
SQL Interface
(DDL, DML, SP, Triggers,
views etc.)
Tools/Utilities
(Backup/restore,
Upgrade, Import,
workbench, replication
etc.)
Parser
(Lexical analysis, Syntactic/
Semantic analysis, parse tree
generation etc.)
Optimizer
(Rewriting queries, order of scan,
plan generation etc.)
Others
MySQL Server
MySQL Connectors
Applications
Plugin Interface
(Daemon, I_S Table, Audit
Log, Query rewrite,
Password validation etc.)
Query Execution
(Sending/retrieving data to/from
SE)
Cache/Buffers
(Query cache, table
cache, etc.)
Disk
Custom
Plugins
MySQL Client
InnoDB
Storage Engines:
CREATE 
FETCH
DELETE
UPDATE
MySQL
Server

MySQL Storage Engines
• Pluggable infrastructure. Write a new SE and plug it in.
• InnoDB : Default SE since MySQL 5.5
• Transactional SE. ACID compliant.
• Row-level-locking, Crash recovery, MVCC.
• Foreign-key referential integrity constraint.
• Different SEs are for different purpose.
7
Introduction

Why InnoDB ?
• ACID compliant.
• High performance/reliability
• Row-level-locking. High concurrency.
• Foreign-key referential integrity
• Flexible with configuration variables to suite individual need.
• Customer/community feedback driven development
• …
8
Benefits

A brief intro
Latest Features
Q&A
9
Agenda

Data Dictionary
• Metadata of tables.
• Earlier :
• InnoDB maintains its own data dictionary for tables in it.
• Meta data information was kept on disk as well in different files (.frm etc).
• Mismatch possible. (b/w InnoDB Dictionary and .frm files on disk)
• Not crash proof.
10
Introduction
SQLs
I_S Tables
InnoDB
Dictionary
Disc
.frm files
.frm files
.frm files

Single New Data Dictionary
• Now :
• One source of truth – System Tables
• Persistent metadata stored in System Tables which are stored in InnoDB.
• Atomic DDL
• No more .frm and InnoDB data dictionary mismatch issues
• Control meta-data access using a single locking mechanism (MDL)
• Server supports the concept of Table-spaces
• .frm files were per table, made tablespace support messy
• All DD tables are in DD table space now.
11
Benefits
SQLs
I_S
Data
Dictionary
DD Tables
System Tables
Views
InnoDB
DD
Tablespace
DD Tables
System Tables

● Upgrade from 5.7 only
● Make sure no crash and previous innodb_fast_shutdown is not set to 2
● Upgrade automatically
● Create new DD tables in DD tablespace
● Update all tables to new DD tables
● Upgrade to the new Undo tablespaces seamlessly
● Create SDI in all the .ibd files.
● Finally, legacy InnoDB system tables are dropped
New Data Dictionary : Upgrade

Serialized Dictionary Information (SDI)
● Purpose
● Redundancy. Metadata stored in the tablespace in addition to the DD
● To make the tablespace self descriptive
● Updated on DDL

SDI tools
• A tool for extracting Serialized Dictionary Information (SDI)
• ibd2sdi
• Works offline and online
• Extracts the SDI data in JSON format
14

Serialized Dictionary Information (SDI)
["ibd2sdi"
,
{
"type": 1,
"id": 340,
"object":
{
…
"dd_object_type": "Table",
"dd_object": {
"name": "t1",
"mysql_version_id": 80019,
"created": 20191104101218,
"last_altered": 20191104101218,
…
"columns": [
{
"name": "id",
"type": 4,
"is_nullable": false,
"is_zerofill": false,
"is_unsigned": false,
"is_auto_increment": false,
…
"schema_ref": “test",
…
"indexes": [
{
"name": "PRIMARY",
"hidden": false,
…
"foreign_keys": [],
"check_constraints": [],
mysql> CREATE TABLE test.t1 (id INT KEY, name CHAR(100));
mayankprasad:~/mysql-bin$ ./bin/ibd2sdi data/test/t1.ibd 
Offline

SDI tools (Example)
• Useful during disaster recovery
• DD info is lost. Only tablespace (ibd) files are available.
• Extract SDI from tablespace (.ibd) file.
• Use SDI to restore table metadata and .ibd to restored data (IMPORT).
• Shared tablespace. One table t1 got corrupted.
• Extract the meta-data from the .ibd file into a separate .SDI file
• Manually edit .SDI file to remove t1 meta-data.
• Use edited .SDI file to import the resining table in tablespace.
16

DDL_log table – For Atomic DDL
• Internal table. Resides in DD tablespace.
• No user DDL/DML allowed in this.
• To support atomic DDL – records physical file actions during DDL.
• A single DDL may generate several entries in this table.
• Changes are persisted immediately, exempted from
innodb_flush_log_at_trx_commit setting.
• Entries are deleted when DDL finishes.
17

DDL_log table – For Atomic DDL
• Records physical changes on disk. Eg : tablespace file creation/drop, index trees
creation/drop, file rename etc.
• These physical operations in a DDL cannot be rolled back by a transaction.
• DDL transaction and this table together, makes Atomic (Crash safe DDL) possible
18

Example – CREATE TABLE with Atomic DDL
MySQL 5.7
• CREATE TABLE T1 …
• InnoDB creates the physical tablespaces/files(file-per-table), Cluster index tree
and other index trees
• InnoDB starts its own transactions to insert new table/indexes metadata to
InnoDB own System tables (note: separate dictionary in InnoDB)
• If server crashes after physical tablespace/files created, before metadata
updated, these files will be orphaned and left behind.

Example – CREATE TABLE with Atomic DDL
MySQL 8.0
• CREATE TABLE T1 …
• InnoDB creates the physical tablespaces/files(file-per-table), Cluster index tree
and other index trees
• InnoDB logs the operations in the DDL_LOG.
• SQL layer commits or rollbacks.
• Call to SE post_ddl(). If rollback, the post_ddl() physically deletes the tablespace/
ibd (file-per-table) and drops the index trees for the table.
• If server crashes, then during DDL recovery ddl_log is consulted to get rid of
orphaned and left behind files.

ALTER TABLE – ADD COLUMN
● Biggest pain point for users
● New columns have to be added (to a big table) from time to time
● Table rebuild was needed. Because each record header keeps columns
specific info.
● Costly - time, disk, resource schedule
● Table lock
● Replication - Master does it. Then slave does the same. Lots of time.
● …

ALTER TABLE - INSTANT ADD COLUMN
● ALTER TABLE t1 ADD COLUMN … ALGORITHM = INSTANT;
● New (default) algorithm
● Internals
● This will result in a metadata change only
● Existing records not touched. No table rebuild required
● Keep new Column’s default in Metadata for existing records.
● No table lock required
● Saves time/space/resources

Table
Old format rows
Old format rows Old format rows
DML
INSERT
DML
UPDATE
ALTER TABLE ..
ADD COLUMN c, [],
ALGORITHM=INSTANT
Data Dictionary
Core DD tables System tables
No update to table!
Number
of fields
Default
values
ALTER TABLE - INSTANT ADD COLUMN

Instant Add Column - Limitations
● Only support adding columns as the last column in the row
● No support for COMPRESSED tables, which is seldom used
● No support for tables with a full-text index
● No support for table residing in DD tablespace
● No support for temporary tables (it goes with COPY)

UNDO Log
● No longer stored in the system table space
● Manage undo logs using SQL
● File names must end in ‘.ibu’ suffix.
● CREATE UNDO TABLESPACE undo001 ADD DATAFILE ‘undo001.ibu’;
● ALTER UNDO TABLESPACE undo001 SET INACTIVE;
● ALTER UNDO TABLESPACE undo001 SET ACTIVE;
● DROP UNDO TABLESPACE undo001;
● Default is two UNDO table spaces

Dedicated Server
• To utilise server resources to max.
• --innodb-dedicated-server := boolean (default OFF)
• Sets values based on physical memory available
• —innodb-log-file-size based on physical memory size
• —innodb-buffer-pool-size based on physical memory size
• —innodb-flush-method = O_DIRECT_NO_FSYNC
• Explicitly set values get preference.

If phy_mem_size < 1G
Use InnoDB default value
Else If phy_mem_size <= 4GB
Use 50% of phy_mem_size
Else
Use 75% of phy_mem_size
End
--innodb-buffer-pool-size
Dedicated Server (contd.) :
If phy_mem_size < 1G
Use InnoDB default value
Else If phy_mem_size <= 4GB
Set to 128 MB
Else if phy_mem_size <= 8 GB
Set to 512 MB
Else if phy_mem_size <= 16 GB
Set to 1GB
Else
Set to 2GB
End
--innodb-log-file-size

Parallel Select Count(*) And Check Table
• Scans the sub-trees below the root node in parallel
• For very large tables it will dynamically break the scan to sub-ranges
• —innodb-parallel-thread-count= [1-256]
• Session variable. Default 4.
• Maximum threads 256.
• Scans partitions in parallel too
• Only works on the clustered index (yet)
• Foundation for future work for all non-locking range selects
• Stay tuned
29

Lock Manager
• Contribution by University of Michigan DB researchers
• Key idea is :
• transaction weight : How it blocks other transactions.
• Allow transaction with more weight to proceed
• Cab driver vs. Bus driver
• No configuration required. Switches b/w FIFO and CATS automatically.
• Threshold is >= 32 waiting Transactions. To make lower contention
work as it is.
30
CATS (Contention Aware Transaction Scheduling)

Lock Manager
• Performance Improvements
• Working on improving CATS 
further.
• 4K -> 15K TPS (512 clients)
• Blog link here
31
CATS (Contention Aware Transaction Scheduling)

Redesigned LOB infrastructure (for DocumentStore)
• For partial fetch and update
• BLOB pages are stored in singly list
• Finding a given offset is time 
and I/O consuming
• Some byte in last page 
of BLOB is to be read in 
very large BLOB.
32
Uncompressed LOBs

• New format
• LOB index pages
• Calculate which page to read 
based on LOB index entries
• Then read that page only.
33
Uncompressed LOBs (contd.)

• Performance Improvement
• 500 Threads (10K->110K)
• Blog link here
34
Uncompressed LOBs (contd.)

• Compressed pages 
stored in singly linked 
list.
• For small update, full 
BLOB is to be  
uncompressed
35
Compressed LOBs

• BLOB divided into chunks
• Chunks are compressed  
separately with index on it.
• For small update, a chunk 
can be found and updated.
36
Compressed LOBs (contd.)

• Improved performance  
results
• Blog link here
37
Compressed LOBs (contd.)

Encryption : Redo/Undo, General Tablespace
• Encrypt redo and undo log
•--innodb-redo-log-encrypt := bool
•--innodb-undo-log-encrypt := bool
• Shared tablespaces
•Support Encryption
•CREATE/ALTER TABLESPACE … ENCRYPTION=‘Y’/’N’
•Support Import/Export using SDI (WIP)

Removed Major I/O bottleneck
• All I/O was covered by a single mutex (fil_sys_t::mutex)
• Sharded the fil_sys_t::mutex
• 64 shards
• Dedicated shard for redo log files and undo tablespaces
39

Performance Results
40
For 512 connections, 600K ->1M TPS.

Lock Free Redo log 
New design (lock free)Old design

Performance Results 
For 256 connections, 60K ->240K TPS.

Clone
• Simple and efficient way to create a MySQL replica
• Cloned replica is a physical snapshot with exact data.
• Can be a cloned locally or remotely
43

Clone
44

Clone
• Configuration parameters are not cloned
• Does not clone binary logs
• Only InnoDB support
• Tables in other storage engines will be cloned as empty tables
• Blocks all concurrent DDLs in Donor node
45

Clone : Observability
• performance_schema.clone_status
• performance_schema.clone_progress
STAGE STATE START TIME DURATION Estimate Done(%)
DROP DATA Completed 17:23:26 790.86 ms 0 MB 100%
FILE COPY Completed 17:23:27 10.33 ms 94,729 MB 100%
PAGE COPY Completed 17:33:47 15.91 s 11,885 MB 100%
REDO COPY Completed 17:34:03 1.07 s 293 MB 100%
FILE SYNC In Progress 17:34:04 51.68 s 0 MB 0%
RESTART Not Started NULL NULL 0 MB 0%
RECOVERY Not Started NULL NULL 0 MB 0%
46

Clone : Resource Control
• Limit network usage
• —clone-max-network-bandwidth (dynamic)
• Affects currently running Clone too
• —clone-enable-compression
• CPU consumption at Donor is going to increase
• Limit data usage
• —clone-max-data-bandwidth (dynamic)
• Set to reduce clone transfer rate to reduce impact
• To control Donor’s performance impact (less I/O).
•
47

Clone : Security
• Secure connection
• CLONE … REQUIRE SSL; — to force secure connection
• For encrypted tablespaces SSL is always enforced
• —clone-ssl* configurations for using certificates
• Clone user at donor instance must have
• Privilege to connect from recipient host user@host
• BACKUP_ADMIN privilege for data copy
• Clone user at recipient must have
• CLONE_ADMIN privilege to replace instance data
• Donor host name and port must be in the recipient configured list
• —clone-valid-donor-list [SYSTEM_VARIABLES_ADMIN privilege is needed]
48

Clone : Performance Control
• Clone plugin uses multiple connections from recipient to donor
server
• —clone-max-concurrency Limits maximum connections
• Helps in preventing CPU/IO/Network saturation 
• Clone starts with 1 thread and threads are increased in steps
• —clone-autotune-concurrency [auto tune spawning threads]
49

Clone : Handles Network Failure
50

Clone : Data Directory
51
• Clone local instance data to a local data directory
mysql> CLONE LOCAL DATA DIRECTORY = “/absolute/path/data”;
• Clone remote instance data
• Instead of replacing current data directory
mysql> CLONE INSTANCE
FROM clone_user@donor.host.com:3306
IDENTIFIED BY “clone_password”
DATA DIRECTORY = “/absolute/path/data”;

Stay tuned to MySQL Server Blogs
http://mysqlserverteam.com
Thank you for using MySQL!

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