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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.
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.
Improving individual query performance
You can test, monitor, and improve queries.
Update statistics when they are not generated automatically
The UPDATE STATISTICS statement updates the statistics in the system catalog tables that the optimizer uses to determine the lowest-cost query plan.
Update statistics in parallel on very large databases
If you have an extremely large database and indexes are fragmented, UPDATE STATISTICS LOW can automatically run statements in parallel.

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.
  - 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.
    - Performance basics
      Performance measurement and tuning issues and methods are relevant to daily database server administration and query execution.
    - Performance monitoring and the tools you use
      You can use performance monitoring tools to create a performance history, to monitor database resources at scheduled times, or to monitor ongoing transaction or query performance.
    - Effect of configuration on CPU utilization
      The combination of operating-system and Informix® configuration parameters can affect CPU utilization. You can change the settings of the Informix configuration parameters that directly affect CPU utilization, and you can adjust the settings for different types of workloads.
    - Effect of configuration on memory utilization
      The combination of operating-system and Informix® configuration parameters can affect memory utilization.
    - Table performance considerations
      Some performance issues are associated with unfragmented tables and table fragments.
    - Boosted Partition Free Space Caches (PFSC)
    - Indexes and index performance considerations
      Informix® provides several types of indexes. Some performance issues are associated with indexes.
    - Locking
      The database server uses locks, which can affect concurrency and performance. You can monitor and administer locks.
    - Fragmentation guidelines
      One of the most frequent causes of poor performance in relational database systems is contention for data that resides on a single I/O device. Proper fragmentation of high-use tables can significantly reduce I/O contention. These topics discuss the performance considerations that are involved when you use table fragmentation.
    - Queries and the query optimizer
      These topics describe query plans, explain how the database server manages query optimization, and discuss factors that you can use to influence the query plan. These topics also describe performance considerations for SPL routines, the UDR cache, and triggers.
    - Optimizer directives
      Optimizer directives are comments that tell the query optimizer how to execute a query. You can use optimizer directives to improve query performance.
    - Parallel database query (PDQ)
      You can manage how the database server performs PDQ and you can monitor the resources that the database server uses for PDQ.
    - Improving individual query performance
      You can test, monitor, and improve queries.
      - Test queries using a dedicated test system
        You can test a query on a system that does not interfere with production database servers. However, you must be careful, because testing queries on a separate system might distort your tuning decisions.
      - Display the query plan
        Before you change a query, display its query plan to determine the kind and amount of resources that the query requires. The query plan shows what parallel scans are used, the maximum number of threads required, and the indexes used.
      - Improve filter selectivity
        You can control the amount of information that a query evaluates. The greater the precision with which you specify the desired rows, the greater the likelihood that your queries will complete quickly.
      - Automatic statistics updating
        The database server updates statistics automatically according to a predefined schedule and a set of expiration policies. The Auto Update Statistics (AUS) maintenance system identifies tables and indexes that require new optimizer statistics and runs the appropriate UPDATE STATISTICS statements to optimize query performance.
      - Update statistics when they are not generated automatically
        The UPDATE STATISTICS statement updates the statistics in the system catalog tables that the optimizer uses to determine the lowest-cost query plan.
        Update the statistics for the number of rows
        When you run UPDATE STATISTICS LOW, the database server updates the statistics in the table, row, and page counts in the system catalog tables. You should run UPDATE STATISTICS LOW as often as necessary to ensure that the statistic for the number of rows is as current as possible.
        Drop data distributions if necessary when upgrading
        When you upgrade to a new version of the database server, you might need to drop distributions to remove the old distribution structure in the sysdistrib system catalog table.
        Creating data distributions
        You can generate statistics for a table and you can build data distributions for each table that your query accesses.
        Updating statistics for join columns
        In some situations, you might want to run the UPDATE STATISTICS statement with the HIGH keyword for specific join columns.
        Updating statistics for columns with user-defined data types
        Programmers can write functions that gather statistics for columns with user-defined data types. You can store the data distributions for user-defined data types in an sbspace.
        Update statistics in parallel on very large databases
        If you have an extremely large database and indexes are fragmented, UPDATE STATISTICS LOW can automatically run statements in parallel.
        Adjust the amount of memory and disk space for UPDATE STATISTICS
        When you execute the UPDATE STATISTICS statement, the database server uses memory and disk to sort and construct data distributions. You can affect the amount of memory and disk space available for UPDATE STATISTICS operations.
        Data sampling during update statistics operations
        If you have a large b-tree index with more than 100 K leaf pages, you can generate index statistics based on sampling when you run UPDATE STATISTICS statements in LOW mode. The gathering of statistics through sampling can increase the speed of the update statistics operation.
        Display data distributions
        You can use the dbschema utility to display data distributions.
      - Improve performance by adding or removing indexes
        You can often improve the performance of a query by adding or, in some cases, removing indexes. You can also enable the optimizer to automatically fetch a set of keys from an index buffer.
      - Optimizer estimates of distributed queries
        The optimizer assumes that access to a row from a remote database takes longer than access to a row in a local database. The optimizer estimates include the cost of retrieving the row from disk and transmitting it across the network.
      - Improve sequential scans
        You can improve the performance of sequential read operations on large tables by eliminating repeated sequential scans.
      - Enable view folding to improve query performance
        You can significantly improve the performance of a query that involves a view by enabling view folding.
      - Reduce the join and sort operations
        After you understand what the query is doing, you can look for ways to obtain the same output with less effort.
      - Optimize user-response time for queries
        You can influence the amount of time that Informix® takes to optimize a query and to return rows to a user.
      - Optimize queries for user-defined data types
        Queries that access user-defined data types (UDTs) can take advantage of the same performance features that built-in data types use.
      - Optimize queries with the SQL statement cache
        Before the database server runs an SQL statement, it must first parse and optimize the statement. Optimizing statements can be time consuming, depending on the size of the SQL statement.
      - Monitor sessions and threads
        You can monitor the number of active sessions and threads and the amount of resources that they are using. Monitoring sessions and threads is important for sessions that perform queries as well as sessions that perform inserts, updates, and deletes.
      - Monitor transactions
        You can monitor transactions to track open transactions and the locks that those transactions hold. You can use several onstat utility options to view transaction, lock, and session statistics.
    - Appendix
  - 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.

Update statistics in parallel on very large databases

If you have an extremely large database and indexes are fragmented, UPDATE STATISTICS LOW can automatically run statements in parallel.

To enable statements to automatically run in parallel, you must run UPDATE STATISTICS LOW with the PDQ priority set to a value that is between 1 and 10. If the PDQ priority is set to 1, 10 percent of the index fragments are analyzed at one time for the current table. If the PDQ priority is set to 5, 50 percent of the index fragments are analyzed at one time for the current table. If the PDQ priority is set to 10, all fragments are analyzed at one time for the current table. (If the PDQ priority is set to a value that is higher than 10, Informix® operates as if the PDQ priority is set to 10, analyzing all fragments at one time for the current table.)

If you run UPDATE STATISTICS MEDIUM or HIGH, you can set the PDQ priority to a value that is higher than 10. Because the UPDATE STATISTICS MEDIUM and HIGH statements perform a large amount of sorting operations, increasing the PDQ priority to a value that is higher than 10 provides additional memory than can improve the speed of the sorting operations.