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Administering
In addition to administering the database server, you can tune performance, replicate data, and archive data.
System administration
These topics contain concepts, procedures, and reference information for database and database server administrators to use for managing and tuning HCL Informix® database servers.
Administrator's Guide
The Informix® Administrator's Guide provides the information required to administer HCL Informix.
Disk, memory, and process management
Shared memory
These topics describe the content of database server shared memory, the factors that determine the sizes of shared-memory areas, and how data moves into and out of shared memory.
Resident portion of shared memory
The operating system, as it switches between the processes that run on the system, normally swaps the contents of portions of memory to disk. When a portion of memory is designated as resident, however, it is not swapped to disk. Keeping frequently accessed data resident in memory improves performance because it reduces the number of disk I/O operations that would otherwise be required to access that data.
Physical-log buffer
The database server uses the physical-log buffer to hold before-images of some of the modified dbspace pages.

Administering
In addition to administering the database server, you can tune performance, replicate data, and archive data.
- System administration
  These topics contain concepts, procedures, and reference information for database and database server administrators to use for managing and tuning HCL Informix® database servers.
  - List of utilities
    HCL Informix® includes utilities and applications that you can use to perform administrative tasks and capture information about configuration and performance.
  - Administrator's Guide
    The Informix® Administrator's Guide provides the information required to administer HCL Informix.
    - The database server
    - Disk, memory, and process management
      - Virtual processors and threads
        These topics describe virtual processors, explain how threads run within the virtual processors, and explain how the database server uses virtual processors and threads to improve performance.
      - Manage virtual processors
        These topics describe how to set the configuration parameters that affect database server virtual processors, and how to start and stop virtual processors.
      - Shared memory
        These topics describe the content of database server shared memory, the factors that determine the sizes of shared-memory areas, and how data moves into and out of shared memory.
        Shared memory
        Shared memory is an operating-system feature that allows the database server threads and processes to share data by sharing access to pools of memory.
        Shared-memory use
        The database server uses shared memory to enable virtual processors and utilities to share data and to provide a fast communications channel for local client applications that use IPC communication.
        Processes that attach to shared memory
        A number of processes attach to the database server shared memory.
        Resident portion of shared memory
        The operating system, as it switches between the processes that run on the system, normally swaps the contents of portions of memory to disk. When a portion of memory is designated as resident, however, it is not swapped to disk. Keeping frequently accessed data resident in memory improves performance because it reduces the number of disk I/O operations that would otherwise be required to access that data.
        Shared-memory header
        The shared-memory header contains a description of all other structures in shared memory, including internal tables and the buffer pool, and pointers to the locations of these structures.
        Shared-memory buffer pool
        The buffer pool in the resident portion of shared memory contains buffers that store dbspace pages read from disk. The pool of buffers comprises the largest allocation of the resident portion of shared memory.
        Logical-log buffer
        The database server uses the logical log to store a record of changes to the database server data since the last dbspace backup. The logical log stores records that represent logical units of work for the database server.
        Physical-log buffer
        The database server uses the physical-log buffer to hold before-images of some of the modified dbspace pages.
        High-Availability Data-Replication buffer
        Data replication requires two instances of the database server, a primary instance and a secondary instance, running on two computers.
        Lock table
        A lock is created when a user thread writes an entry in the lock table. A single transaction can own multiple locks. The lock table is the pool of available locks.
        Buffer pool portion of shared memory
        The buffer pool portion of shared memory contains the buffers that store dbspace pages that are read from disk.
        Virtual portion of shared memory
        The virtual portion of shared memory is expandable by the database server and can be paged out to disk by the operating system.
        Communications portion of shared memory (UNIX™)
        The database server allocates memory for the IPC communication portion of shared memory if you configure at least one of your connections as an IPC shared-memory connection. The database server performs this allocation when you set up shared memory.
        Virtual-extension portion of shared memory
        The virtual-extension portion of shared memory contains additional virtual segments and virtual-extension segments.
        Concurrency control
        The database server threads that run on the same virtual processor and on separate virtual processors share access to resources in shared memory.
        Database server thread access to shared buffers
        Database server threads access shared buffers through a system of queues, using mutexes and locks to synchronize access and protect data.
        Flush data to disk
        Writing a buffer to disk is called buffer flushing.
        Buffer large-object data
        Simple large objects (TEXT or BYTE data) can be stored in either dbspaces or blobspaces. Smart large objects (CLOB or BLOB data) are stored only in sbspaces.
        Memory use on 64-bit platforms
        With 64-bit addressing, you can have larger buffer pools to reduce the amount of I/O operations to obtain data from disks.
      - Manage shared memory
      - Data storage
        The database server uses physical units of storage to allocate disk space. It stores data in logical units. Unlike the logical units of storage whose size fluctuates, each of the physical units has a fixed or assigned size that is determined by the disk architecture.
      - Manage disk space
        You can use several utilities and tools to manage disk spaces and the data that the database server controls.
      - Moving data with external tables
        You can use external tables to load and unload database data.
      - Storage space encryption
        You can encrypt storage spaces (dbspaces, blobspaces and smart blobspaces) with Informix Dynamic Server. The data in encrypted storage spaces is unintelligible without the encryption key. Encrypting storage spaces is an effective way to protect sensitive information that is stored on disk.
    - Logging and log administration
    - Fault tolerance
    - High availability and scalability
      A successful production environment requires database systems that are always available, with minimal if any planned outages, and that can be scaled quickly and easily as business requirements change.
    - Distributed data
    - Overview of automatic monitoring and corrective actions
      You can use the SQL administration API, the Scheduler, and drill-down queries to manage automatic maintenance, monitoring, and administrative tasks.
  - Administrator's Reference
    The Informix® Administrator's Reference includes comprehensive descriptions of HCL Informix configuration parameters, the system-monitoring interface (SMI) tables in the sysmaster database, the syntax of database server utilities such as onmode and onstat, logical-log records, disk structures, event alarms, and unnumbered error messages.
  - DB-Access User's Guide
    The Informix® DB-Access User's Guide describes how to use the DB-Access utility to access, modify, and retrieve information from Informix database servers.
  - High-Performance Loader User's Guide
    The describes how to use the HCL Informix® to load and unload large quantities of data efficiently to or from Informix databases.
  - Performance Guide
    The Informix® Performance Guide describes how to configure and operate your HCL Informix database server to improve overall system throughput and to improve the performance of SQL queries.
  - SNMP Subagent Guide
    The describes the Simple Network Management Protocol (SNMP) and the software that you need to use SNMP to monitor and manage HCL Informix® database servers and databases.
  - InformixHQ Guide
    InformixHQ is a modern web console for visualizing, monitoring, and managing your Informix server instances. It is purpose built for ease-of-use, scaling out, and optimizing DevOps needs. It provides critical performance management capabilities, monitoring how key performance metrics are changing over time and tracking how efficiently Informix is running your workload even when you’ve stepped away from your screen. Its monitoring system feeds directly into a customizable alerting system so you can be immediately alerted via email, Twilio, or PagerDuty whenever an issue occurs on one of your Informix database server instances. InformixHQ is designed to be scalable to efficiently manage and monitor as many Informix database server instances as you need. Moreover, it's a tool that can be shared by the DBAs, the app developers, the ops engineers, and management and accessed from any desktop, laptop, or mobile device. InformixHQ is the centralized hub for graphical monitoring, alerting, and administration of your Informix database servers.
- Backup and Restore Guide
  The Informix® Backup and Restore Guide describes how to use the Informix ON-Bar and ontape utilities to back up and restore database server data. These utilities enable you to recover your databases after data is lost or becomes corrupted due to hardware or software failure or accident.
- Enterprise Replication
  The HCL® Informix® Enterprise Replication Guide describes the concepts of data replication using Informix Enterprise Replication, including how to design your replication system, as well as administer and manage data replication throughout your enterprise.

Physical-log buffer

The database server uses the physical-log buffer to hold before-images of some of the modified dbspace pages.

The before-images in the physical log and the logical-log records enable the database server to restore consistency to its databases after a system failure.

The physical-log buffer is actually two buffers. Double buffering permits the database server processes to write to the active physical-log buffer while the other buffer is being flushed to the physical log on disk. For a description of how the database server flushes the physical-log buffer, see Flush the physical-log buffer. For information about monitoring the physical-log file, see Monitor physical and logical-logging activity.

The PHYSBUFF parameter in the onconfig file specifies the size of the physical-log buffers. A write to the physical-log buffer writes exactly one page. If the specified size of the physical-log buffer is not evenly divisible by the page size, the database server rounds the size down to the nearest value that is evenly divisible by the page size. Although some operations require the buffer to be flushed sooner, in general the database server flushes the buffer to the physical-log file on disk when the buffer fills. Thus, the size of the buffer determines how frequently the database server must flush it to disk.

The default value for the physical log buffer size is 512 KB. If you decide to use a smaller value, the database server displays a message indicating that optimal performance might not be attained. Using a physical log buffer smaller than 512 KB affects performance only, not transaction integrity.

For more information about this configuration parameter, see the Informix® Administrator's Reference.