- About MogDB
- MogDB Introduction
- Comparison Between MogDB and openGauss
- MogDB Release Note
- High Availability and Performance
- Open Source Components
- Usage Limitations
- Terms of Use
- Quick Start
- Installation Guide
- Container Installation
- Standard Installation
- Installation Overview
- Preparing for Installation
- Installing the MogDB
- Verifying the Installation
- Uninstalling the MogDB
- Administrator Guide
- Routine Maintenance
- Primary and Standby Management
- MogHA Management
- MOT Engine
- Introducing MOT
- Using MOT
- Concepts of MOT
- Appendix
- Column-store Tables Management
- Backup and Restoration
- Importing and Exporting Data
- Importing Data
- Exporting Data
- Upgrade Guide
- Common Fault Locating Cases
- Core Fault Locating
- When the TPC-C is running and a disk to be injected is full, the TPC-C stops responding
- Standby Node in the Need Repair (WAL) State
- Insufficient Memory
- Service Startup Failure
- "Error:No space left on device" Is Displayed
- After You Run the du Command to Query Data File Size In the XFS File System, the Query Result Is Greater than the Actual File Size
- File Is Damaged in the XFS File System
- Primary Node Is Hung in Demoting During a Switchover
- Disk Space Usage Reaches the Threshold and the Database Becomes Read-only
- Slow Response to a Query Statement
- Analyzing the Status of a Query Statement
- Forcibly Terminating a Session
- Analyzing Whether a Query Statement Is Blocked
- Low Query Efficiency
- "Lock wait timeout" Is Displayed When a User Executes an SQL Statement
- Table Size Does not Change After VACUUM FULL Is Executed on the Table
- An Error Is Reported When the Table Partition Is Modified
- Different Data Is Displayed for the Same Table Queried By Multiple Users
- When a User Specifies Only an Index Name to Modify the Index, A Message Indicating That the Index Does Not Exist Is Displayed
- Reindexing Fails
- An Error Occurs During Integer Conversion
- "too many clients already" Is Reported or Threads Failed To Be Created in High Concurrency Scenarios
- B-tree Index Faults
- Security Guide
- Database Security Management
- Performance Tuning
- System Optimization
- SQL Optimization
- WDR Snapshot Schema
- Developer Guide
- Application Development Guide
- Development Specifications
- Development Based on JDBC
- Overview
- JDBC Package, Driver Class, and Environment Class
- Development Process
- Loading the Driver
- Connecting to a Database
- Connecting to the Database (Using SSL)
- Running SQL Statements
- Processing Data in a Result Set
- Closing a Connection
- Example: Common Operations
- Example: Retrying SQL Queries for Applications
- Example: Importing and Exporting Data Through Local Files
- Example 2: Migrating Data from a MY Database to MogDB
- Example: Logic Replication Code
- JDBC Interface Reference
- Development Based on ODBC
- Development Based on libpq
- Commissioning
- Appendices
- Stored Procedure
- User Defined Functions
- Application Development Guide
- Tool Reference
- System Catalogs and System Views
- Overview of System Catalogs and System Views
- System Catalogs
- GS_CLIENT_GLOBAL_KEYS
- GS_CLIENT_GLOBAL_KEYS_ARGS
- GS_COLUMN_KEYS
- GS_COLUMN_KEYS_ARGS
- GS_ENCRYPTED_COLUMNS
- GS_OPT_MODEL
- GS_WLM_INSTANCE_HISTORY
- GS_WLM_OPERATOR_INFO
- GS_WLM_PLAN_ENCODING_TABLE
- GS_WLM_PLAN_OPERATOR_INFO
- GS_WLM_USER_RESOURCE_HISTORY
- PG_AGGREGATE
- PG_AM
- PG_AMOP
- PG_AMPROC
- PG_APP_WORKLOADGROUP_MAPPING
- PG_ATTRDEF
- PG_ATTRIBUTE
- PG_AUTHID
- PG_AUTH_HISTORY
- PG_AUTH_MEMBERS
- PG_CAST
- PG_CLASS
- PG_COLLATION
- PG_CONSTRAINT
- PG_CONVERSION
- PG_DATABASE
- PG_DB_ROLE_SETTING
- PG_DEFAULT_ACL
- PG_DEPEND
- PG_DESCRIPTION
- PG_DIRECTORY
- PG_ENUM
- PG_EXTENSION
- PG_EXTENSION_DATA_SOURCE
- PG_FOREIGN_DATA_WRAPPER
- PG_FOREIGN_SERVER
- PG_FOREIGN_TABLE
- PG_INDEX
- PG_INHERITS
- PG_JOB
- PG_JOB_PROC
- PG_LANGUAGE
- PG_LARGEOBJECT
- PG_LARGEOBJECT_METADATA
- PG_NAMESPACE
- PG_OBJECT
- PG_OPCLASS
- PG_OPERATOR
- PG_OPFAMILY
- PG_PARTITION
- PG_PLTEMPLATE
- PG_PROC
- PG_RANGE
- PG_RESOURCE_POOL
- PG_REWRITE
- PG_RLSPOLICY
- PG_SECLABEL
- PG_SHDEPEND
- PG_SHDESCRIPTION
- PG_SHSECLABEL
- PG_STATISTIC
- PG_STATISTIC_EXT
- PG_TABLESPACE
- PG_TRIGGER
- PG_TS_CONFIG
- PG_TS_CONFIG_MAP
- PG_TS_DICT
- PG_TS_PARSER
- PG_TS_TEMPLATE
- PG_TYPE
- PG_USER_MAPPING
- PG_USER_STATUS
- PG_WORKLOAD_GROUP
- PLAN_TABLE_DATA
- STATEMENT_HISTORY
- System Views
- GS_SESSION_CPU_STATISTICS
- GS_SESSION_MEMORY_STATISTICS
- GS_SQL_COUNT
- GS_WLM_OPERATOR_HISTORY
- GS_WLM_OPERATOR_STATISTICS
- GS_WLM_PLAN_OPERATOR_HISTORY
- GS_WLM_REBUILD_USER_RESOURCE_POOL
- GS_WLM_RESOURCE_POOL
- GS_WLM_SESSION_HISTORY
- GS_WLM_SESSION_INFO_ALL
- GS_WLM_USER_INFO
- GS_WLM_SESSION_STATISTICS
- GS_STAT_SESSION_CU
- MPP_TABLES
- PG_AVAILABLE_EXTENSION_VERSIONS
- PG_AVAILABLE_EXTENSIONS
- PG_CURSORS
- PG_EXT_STATS
- PG_GET_INVALID_BACKENDS
- PG_GET_SENDERS_CATCHUP_TIME
- PG_GROUP
- PG_GTT_RELSTATS
- PG_GTT_STATS
- PG_GTT_ATTACHED_PIDS
- PG_INDEXES
- PG_LOCKS
- PG_MATVIEWS
- PG_NODE_ENV
- PG_OS_THREADS
- PG_PREPARED_STATEMENTS
- PG_PREPARED_XACTS
- PG_REPLICATION_SLOTS
- PG_RLSPOLICIES
- PG_ROLES
- PG_RULES
- PG_SECLABELS
- PG_SESSION_WLMSTAT
- PG_SESSION_IOSTAT
- PG_SETTINGS
- PG_SHADOW
- PG_STATS
- PG_STAT_ACTIVITY
- PG_STAT_ALL_INDEXES
- PG_STAT_ALL_TABLES
- PG_STAT_BAD_BLOCK
- PG_STAT_BGWRITER
- PG_STAT_DATABASE
- PG_STAT_DATABASE_CONFLICTS
- PG_STAT_USER_FUNCTIONS
- PG_STAT_USER_INDEXES
- PG_STAT_USER_TABLES
- PG_STAT_REPLICATION
- PG_STAT_SYS_INDEXES
- PG_STAT_SYS_TABLES
- PG_STAT_XACT_ALL_TABLES
- PG_STAT_XACT_SYS_TABLES
- PG_STAT_XACT_USER_FUNCTIONS
- PG_STAT_XACT_USER_TABLES
- PG_STATIO_ALL_INDEXES
- PG_STATIO_ALL_SEQUENCES
- PG_STATIO_ALL_TABLES
- PG_STATIO_SYS_INDEXES
- PG_STATIO_SYS_SEQUENCES
- PG_STATIO_SYS_TABLES
- PG_STATIO_USER_INDEXES
- PG_STATIO_USER_SEQUENCES
- PG_STATIO_USER_TABLES
- PG_THREAD_WAIT_STATUS
- PG_TABLES
- PG_TDE_INFO
- PG_TIMEZONE_NAMES
- PG_TOTAL_USER_RESOURCE_INFO
- PG_USER
- PG_USER_MAPPINGS
- PG_VIEWS
- PG_WLM_STATISTICS
- PLAN_TABLE
- GS_FILE_STAT
- GS_OS_RUN_INFO
- GS_REDO_STAT
- GS_SESSION_MEMORY
- GS_SESSION_MEMORY_DETAIL
- GS_SESSION_STAT
- GS_SESSION_TIME
- GS_THREAD_MEMORY_DETAIL
- GS_TOTAL_MEMORY_DETAIL
- PG_TIMEZONE_ABBREVS
- PG_TOTAL_USER_RESOURCE_INFO_OID
- PG_VARIABLE_INFO
- GS_INSTANCE_TIME
- Functions and Operators
- Logical Operators
- Comparison Operators
- Character Processing Functions and Operators
- Binary String Functions and Operators
- Bit String Functions and Operators
- Mode Matching Operators
- Mathematical Functions and Operators
- Date and Time Processing Functions and Operators
- Type Conversion Functions
- Geometric Functions and Operators
- Network Address Functions and Operators
- Text Search Functions and Operators
- JSON Functions
- SEQUENCE Functions
- Array Functions and Operators
- Range Functions and Operators
- Aggregate Functions
- Window Functions
- Security Functions
- Encrypted Equality Functions
- Set Returning Functions
- Conditional Expression Functions
- System Information Functions
- System Administration Functions
- Statistics Information Functions
- Trigger Functions
- Global Temporary Table Functions
- AI Feature Functions
- Other System Functions
- Supported Data Types
- SQL Syntax
- ABORT
- ALTER DATABASE
- ALTER DATA SOURCE
- ALTER DEFAULT PRIVILEGES
- ALTER DIRECTORY
- ALTER FOREIGN TABLE
- ALTER FUNCTION
- ALTER GROUP
- ALTER INDEX
- ALTER LARGE OBJECT
- ALTER MATERIALIZED VIEW
- ALTER ROLE
- ALTER ROW LEVEL SECURITY POLICY
- ALTER RULE
- ALTER SCHEMA
- ALTER SEQUENCE
- ALTER SERVER
- ALTER SESSION
- ALTER SYNONYM
- ALTER SYSTEM KILL SESSION
- ALTER SYSTEM SET
- ALTER TABLE
- ALTER TABLE PARTITION
- ALTER TABLESPACE
- ALTER TEXT SEARCH CONFIGURATION
- ALTER TEXT SEARCH DICTIONARY
- ALTER TRIGGER
- ALTER TYPE
- ALTER USER
- ALTER USER MAPPING
- ALTER VIEW
- ANALYZE | ANALYSE
- BEGIN
- CALL
- CHECKPOINT
- CLOSE
- CLUSTER
- COMMENT
- COMMIT | END
- COMMIT PREPARED
- COPY
- CREATE CLIENT MASTER KEY
- CREATE COLUMN ENCRYPTION KEY
- CREATE DATABASE
- CREATE DATA SOURCE
- CREATE DIRECTORY
- CREATE FOREIGN TABLE
- CREATE FUNCTION
- CREATE GROUP
- CREATE INDEX
- CREATE MATERIALIZED VIEW
- CREATE ROW LEVEL SECURITY POLICY
- CREATE PROCEDURE
- CREATE ROLE
- CREATE RULE
- CREATE SCHEMA
- CREATE SEQUENCE
- CREATE SERVER
- CREATE SYNONYM
- CREATE TABLE
- CREATE TABLE AS
- CREATE TABLE PARTITION
- CREATE TABLESPACE
- CREATE TEXT SEARCH CONFIGURATION
- CREATE TEXT SEARCH DICTIONARY
- CREATE TRIGGER
- CREATE TYPE
- CREATE USER
- CREATE USER MAPPING
- CREATE VIEW
- CURSOR
- DEALLOCATE
- DECLARE
- DELETE
- DO
- DROP CLIENT MASTER KEY
- DROP COLUMN ENCRYPTION KEY
- DROP DATABASE
- DROP DATA SOURCE
- DROP DIRECTORY
- DROP FOREIGN TABLE
- DROP FUNCTION
- DROP GROUP
- DROP INDEX
- DROP MATERIALIZED VIEW
- DROP OWNED
- DROP ROW LEVEL SECURITY POLICY
- DROP PROCEDURE
- DROP ROLE
- DROP RULE
- DROP SCHEMA
- DROP SEQUENCE
- DROP SERVER
- DROP SYNONYM
- DROP TABLE
- DROP TABLESPACE
- DROP TEXT SEARCH CONFIGURATION
- DROP TEXT SEARCH DICTIONARY
- DROP TRIGGER
- DROP TYPE
- DROP USER
- DROP USER MAPPING
- DROP VIEW
- EXECUTE
- EXPLAIN
- EXPLAIN PLAN
- FETCH
- GRANT
- INSERT
- LOCK
- MOVE
- MERGE INTO
- PREPARE
- PREPARE TRANSACTION
- REASSIGN OWNED
- REFRESH MATERIALIZED VIEW
- REINDEX
- RELEASE SAVEPOINT
- RESET
- REVOKE
- ROLLBACK
- ROLLBACK PREPARED
- ROLLBACK TO SAVEPOINT
- SAVEPOINT
- SELECT
- SELECT INTO
- SET
- SET CONSTRAINTS
- SET ROLE
- SET SESSION AUTHORIZATION
- SET TRANSACTION
- SHOW
- SHUTDOW
- START TRANSACTION
- TRUNCATE
- UPDATE
- VACUUM
- VALUES
- GUC Parameters
- GUC Parameter Usage
- File Location
- Connection and Authentication
- Resource Consumption
- Parallel Import
- Write Ahead Log
- HA Replication
- Memory Table
- Query Planning
- Error Reporting and Logging
- Alarm Detection
- Statistics During the Database Running
- Load Management
- Automatic Vacuuming
- Default Settings of Client Connection
- Lock Management
- Version and Platform Compatibility
- Faut Tolerance
- Connection Pool Parameters
- MogDB Transaction
- Developer Options
- Auditing
- Upgrade Parameters
- Miscellaneous Parameters
- Wait Events
- Query
- System Performance Snapshot
- Equality Query in a Fully-encrypted Database
- Global Temporary Table
- Appendix
- DBE_PERF
- DBE_PERF Overview
- OS
- Instance
- Memory
- File
- Object
- STAT_USER_TABLES
- SUMMARY_STAT_USER_TABLES
- GLOBAL_STAT_USER_TABLES
- STAT_USER_INDEXES
- SUMMARY_STAT_USER_INDEXES
- GLOBAL_STAT_USER_INDEXES
- STAT_SYS_TABLES
- SUMMARY_STAT_SYS_TABLES
- GLOBAL_STAT_SYS_TABLES
- STAT_SYS_INDEXES
- SUMMARY_STAT_SYS_INDEXES
- GLOBAL_STAT_SYS_INDEXES
- STAT_ALL_TABLES
- SUMMARY_STAT_ALL_TABLES
- GLOBAL_STAT_ALL_TABLES
- STAT_ALL_INDEXES
- SUMMARY_STAT_ALL_INDEXES
- GLOBAL_STAT_ALL_INDEXES
- STAT_DATABASE
- SUMMARY_STAT_DATABASE
- GLOBAL_STAT_DATABASE
- STAT_DATABASE_CONFLICTS
- SUMMARY_STAT_DATABASE_CONFLICTS
- GLOBAL_STAT_DATABASE_CONFLICTS
- STAT_XACT_ALL_TABLES
- SUMMARY_STAT_XACT_ALL_TABLES
- GLOBAL_STAT_XACT_ALL_TABLES
- STAT_XACT_SYS_TABLES
- SUMMARY_STAT_XACT_SYS_TABLES
- GLOBAL_STAT_XACT_SYS_TABLES
- STAT_XACT_USER_TABLES
- SUMMARY_STAT_XACT_USER_TABLES
- GLOBAL_STAT_XACT_USER_TABLES
- STAT_XACT_USER_FUNCTIONS
- SUMMARY_STAT_XACT_USER_FUNCTIONS
- GLOBAL_STAT_XACT_USER_FUNCTIONS
- STAT_BAD_BLOCK
- SUMMARY_STAT_BAD_BLOCK
- GLOBAL_STAT_BAD_BLOCK
- STAT_USER_FUNCTIONS
- SUMMARY_STAT_USER_FUNCTIONS
- GLOBAL_STAT_USER_FUNCTIONS
- Workload
- Session/Thread
- SESSION_STAT
- GLOBAL_SESSION_STAT
- SESSION_TIME
- GLOBAL_SESSION_TIME
- SESSION_MEMORY
- GLOBAL_SESSION_MEMORY
- SESSION_MEMORY_DETAIL
- GLOBAL_SESSION_MEMORY_DETAIL
- SESSION_STAT_ACTIVITY
- GLOBAL_SESSION_STAT_ACTIVITY
- THREAD_WAIT_STATUS
- GLOBAL_THREAD_WAIT_STATUS
- LOCAL_THREADPOOL_STATUS
- GLOBAL_THREADPOOL_STATUS
- SESSION_CPU_RUNTIME
- SESSION_MEMORY_RUNTIME
- STATEMENT_IOSTAT_COMPLEX_RUNTIME
- Transaction
- Query
- STATEMENT
- SUMMARY_STATEMENT
- STATEMENT_COUNT
- GLOBAL_STATEMENT_COUNT
- SUMMARY_STATEMENT_COUNT
- GLOBAL_STATEMENT_COMPLEX_HISTORY
- GLOBAL_STATEMENT_COMPLEX_HISTORY_TABLE
- GLOBAL_STATEMENT_COMPLEX_RUNTIME
- STATEMENT_RESPONSETIME_PERCENTILE
- STATEMENT_USER_COMPLEX_HISTORY
- STATEMENT_COMPLEX_RUNTIME
- STATEMENT_COMPLEX_HISTORY_TABLE
- STATEMENT_COMPLEX_HISTORY
- STATEMENT_WLMSTAT_COMPLEX_RUNTIME
- STATEMENT_HISTORY
- Cache/IO
- STATIO_USER_TABLES
- SUMMARY_STATIO_USER_TABLES
- GLOBAL_STATIO_USER_TABLES
- STATIO_USER_INDEXES
- SUMMARY_STATIO_USER_INDEXES
- GLOBAL_STATIO_USER_INDEXES
- STATIO_USER_SEQUENCES
- SUMMARY_STATIO_USER_SEQUENCES
- GLOBAL_STATIO_USER_SEQUENCES
- STATIO_SYS_TABLES
- SUMMARY_STATIO_SYS_TABLES
- GLOBAL_STATIO_SYS_TABLES
- STATIO_SYS_INDEXES
- SUMMARY_STATIO_SYS_INDEXES
- GLOBAL_STATIO_SYS_INDEXES
- STATIO_SYS_SEQUENCES
- SUMMARY_STATIO_SYS_SEQUENCES
- GLOBAL_STATIO_SYS_SEQUENCES
- STATIO_ALL_TABLES
- SUMMARY_STATIO_ALL_TABLES
- GLOBAL_STATIO_ALL_TABLES
- STATIO_ALL_INDEXES
- SUMMARY_STATIO_ALL_INDEXES
- GLOBAL_STATIO_ALL_INDEXES
- STATIO_ALL_SEQUENCES
- SUMMARY_STATIO_ALL_SEQUENCES
- GLOBAL_STATIO_ALL_SEQUENCES
- GLOBAL_STAT_DB_CU
- GLOBAL_STAT_SESSION_CU
- Utility
- REPLICATION_STAT
- GLOBAL_REPLICATION_STAT
- REPLICATION_SLOTS
- GLOBAL_REPLICATION_SLOTS
- BGWRITER_STAT
- GLOBAL_BGWRITER_STAT
- GLOBAL_CKPT_STATUS
- GLOBAL_DOUBLE_WRITE_STATUS
- GLOBAL_PAGEWRITER_STATUS
- GLOBAL_RECORD_RESET_TIME
- GLOBAL_REDO_STATUS
- GLOBAL_RECOVERY_STATUS
- CLASS_VITAL_INFO
- USER_LOGIN
- SUMMARY_USER_LOGIN
- GLOBAL_GET_BGWRITER_STATUS
- Lock
- Wait Events
- Configuration
- Operator
- Workload Manager
- Global Plancache
- Appendix
- Error Code Reference
- Description of SQL Error Codes
- Third-Party Library Error Codes
- GAUSS-00001 - GAUSS-00100
- GAUSS-00101 - GAUSS-00200
- GAUSS 00201 - GAUSS 00300
- GAUSS 00301 - GAUSS 00400
- GAUSS 00401 - GAUSS 00500
- GAUSS 00501 - GAUSS 00600
- GAUSS 00601 - GAUSS 00700
- GAUSS 00701 - GAUSS 00800
- GAUSS 00801 - GAUSS 00900
- GAUSS 00901 - GAUSS 01000
- GAUSS 01001 - GAUSS 01100
- GAUSS 01101 - GAUSS 01200
- GAUSS 01201 - GAUSS 01300
- GAUSS 01301 - GAUSS 01400
- GAUSS 01401 - GAUSS 01500
- GAUSS 01501 - GAUSS 01600
- GAUSS 01601 - GAUSS 01700
- GAUSS 01701 - GAUSS 01800
- GAUSS 01801 - GAUSS 01900
- GAUSS 01901 - GAUSS 02000
- GAUSS 02001 - GAUSS 02100
- GAUSS 02101 - GAUSS 02200
- GAUSS 02201 - GAUSS 02300
- GAUSS 02301 - GAUSS 02400
- GAUSS 02401 - GAUSS 02500
- GAUSS 02501 - GAUSS 02600
- GAUSS 02601 - GAUSS 02700
- GAUSS 02701 - GAUSS 02800
- GAUSS 02801 - GAUSS 02900
- GAUSS 02901 - GAUSS 03000
- GAUSS 03001 - GAUSS 03100
- GAUSS 03101 - GAUSS 03200
- GAUSS 03201 - GAUSS 03300
- GAUSS 03301 - GAUSS 03400
- GAUSS 03401 - GAUSS 03500
- GAUSS 03501 - GAUSS 03600
- GAUSS 03601 - GAUSS 03700
- GAUSS 03701 - GAUSS 03800
- GAUSS 03801 - GAUSS 03900
- GAUSS 03901 - GAUSS 04000
- GAUSS 04001 - GAUSS 04100
- GAUSS 04101 - GAUSS 04200
- GAUSS 04201 - GAUSS 04300
- GAUSS 04301 - GAUSS 04400
- GAUSS 04401 - GAUSS 04500
- GAUSS 04501 - GAUSS 04600
- GAUSS 04601 - GAUSS 04700
- GAUSS 04701 - GAUSS 04800
- GAUSS 04801 - GAUSS 04900
- GAUSS 04901 - GAUSS 05000
- GAUSS 05001 - GAUSS 05100
- GAUSS 05101 - GAUSS 05200
- GAUSS 05201 - GAUSS 05300
- GAUSS 05301 - GAUSS 05400
- GAUSS 05401 - GAUSS 05500
- GAUSS 05501 - GAUSS 05600
- GAUSS 05601 - GAUSS 05700
- GAUSS 05701 - GAUSS 05800
- GAUSS 05801 - GAUSS 05900
- GAUSS 05901 - GAUSS 06000
- GAUSS 06001 - GAUSS 06100
- GAUSS 06101 - GAUSS 06200
- GAUSS 06201 - GAUSS 06300
- GAUSS 06301 - GAUSS 06400
- GAUSS 06401 - GAUSS 06500
- GAUSS 06501 - GAUSS 06600
- GAUSS 06601 - GAUSS 06700
- GAUSS 06701 - GAUSS 06800
- GAUSS 06801 - GAUSS 06900
- GAUSS 06901 - GAUSS 07000
- GAUSS 07001 - GAUSS 07100
- GAUSS 07101 - GAUSS 07200
- GAUSS 07201 - GAUSS 07300
- GAUSS 07301 - GAUSS 07400
- GAUSS 07401 - GAUSS 07480
- GAUSS 50000 - GAUSS 50999
- GAUSS 51000 - GAUSS 51999
- GAUSS 52000 - GAUSS 52999
- GAUSS 53000 - GAUSS 53699
- System Catalogs and System Views
- Glossary
MOT Query Native Compilation (JIT)
MOT enables you to prepare and parse pre-compiled full queries in a native format (using a PREPARE statement) before they are needed for execution.
This native format can later be executed (using an EXECUTE command) more efficiently. This type of execution is much more efficient because during execution the native format bypasses multiple database processing layers. This division of labor avoids repetitive parse analysis operations. The Lite Executor module is responsible for executing prepared queries and has a much faster execution path than the regular generic plan performed by the envelope. This is achieved using Just-In-Time (JIT) compilation via LLVM. In addition, a similar solution that has potentially similar performance is provided in the form of pseudo-LLVM.
The following is an example of a PREPARE syntax in SQL -
PREPARE name [ ( data_type [, ...] ) ] AS statement
The following is an example of how to invoke a PREPARE and then an EXECUTE statement in a Java application -
conn = DriverManager.getConnection(connectionUrl, connectionUser, connectionPassword);
// Example 1: PREPARE without bind settings
String query = "SELECT * FROM getusers";
PreparedStatement prepStmt1 = conn.prepareStatement(query);
ResultSet rs1 = pstatement.executeQuery())
while (rs1.next()) {…}
// Example 2: PREPARE with bind settings
String sqlStmt = "SELECT * FROM employees where first_name=? and last_name like ?";
PreparedStatement prepStmt2 = conn.prepareStatement(sqlStmt);
prepStmt2.setString(1, "Mark"); // first name "Mark"
prepStmt2.setString(2, "%n%"); // last name contains a letter "n"
ResultSet rs2 = prepStmt2.executeQuery())
while (rs2.next()) {…}
Prepare
PREPARE creates a prepared statement. A prepared statement is a server-side object that can be used to optimize performance. When the PREPARE statement is executed, the specified statement is parsed, analyzed and rewritten.
If the tables mentioned in the query statement are MOT tables, the MOT compilation takes charge of the object preparation and performs a special optimization by compiling the query into IR byte code based on LLVM.
Whenever a new query compilation is required, the query is analyzed and a proper tailored IR byte code is generated for the query using the utility GsCodeGen object and standard LLVM JIT API (IRBuilder). After byte-code generation is completed, the code is JIT-compiled into a separate LLVM module. The compiled code results in a C function pointer that can later be invoked for direct execution. Note that this C function can be invoked concurrently by many threads, as long as each thread provides a distinct execution context (details are provided below). Each such execution context is referred to as JIT Context.
To improve performance further, MOT JIT applies a caching policy for its LLVM code results, enabling them to be reused for the same queries across different sessions.
Execute
When an EXECUTE command is issued, the prepared statement (described above) is planned and executed. This division of labor avoids repetitive parse analysis work, while enabling the execution plan to depend on the specific setting values supplied.
When the resulting execute query command reaches the database, it uses the corresponding IR byte code which is executed directly and more efficiently within the MOT engine. This is referred to as Lite Execution.
In addition, for availability, the Lite Executor maintains a preallocated pool of JIT sources. Each session preallocates its own session-local pool of JIT context objects (used for repeated executions of precompiled queries).
For more details you may refer to the Supported Queries for Lite Execution and Unsupported Queries for Lite Execution sections.
JIT Compilation Comparison - MogDB Disk-based vs. MOT Tables
Currently, MogDB contains two main forms of JIT / CodeGen query optimizations for its disk-based tables -
- Accelerating expression evaluation, such as in WHERE clauses, target lists, aggregates and projections
- Inlining small function invocations.
These optimizations are partial (in the sense they do not optimize the entire interpreted operator tree or replace it altogether) and are targeted mostly at CPU-bound complex queries, typically seen in OLAP use cases. The execution of queries is performed in a pull-model (Volcano-style processing) using an interpreted operator tree. When activated, the compilation is performed at each query execution. At the moment, caching of the generated LLVM code and its reuse across sessions and queries is not yet provided.
In contrast, MOT JIT optimization provides LLVM code for entire queries that qualify for JIT optimization by MOT. The resulting code is used for direct execution over MOT tables, while the interpreted operator model is abandoned completely. The result is practically handwritten LLVM code that has been generated for an entire specific query execution.
Another significant conceptual difference is that MOT LLVM code is only generated for prepared queries during the PREPARE phase of the query, rather than at query execution. This is especially important for OLTP scenarios due to the rather short runtime of OLTP queries, which cannot allow for code generation and relatively long query compilation time to be performed during each query execution.
Finally, in PostgreSQL the activation of a PREPARE implies the reuse of the resulting plan across executions with different parameters in the same session. Similarly, the MOT JIT applies a caching policy for its LLVM code results, and extends it for reuse across different sessions. Thus, a single query may be compiled just once and its LLVM code may be reused across many sessions, which again is beneficial for OLTP scenarios.