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Oracle x$ tables

Oracle Database Tips by Burleson Consulting

Question:  Why are the Oracle x$ tables hidden?

Answer:  Oracle builds v$ views upon the Oracle x$ tables (which are actually mapped in-memory C program structures) and the x$ tables and columns, while interesting are undocumented and change with each release.

Here is a description of some of the Oracle x$ tables and sample queries against the x$ table structures.  You can also grep your $ORACLE_HOME/rdbms/admin directory and see how the x$ structures are mapped to v$ views.

Also see the x$ kernel service & cache table.

For a map of the important data on the v$ views that are built from the Oracle x$ tables, see this Oracle Poster.

Exploring Oracle Internals - Inside the x$ Tables of Oracle 11g

The power inherent in the dynamic performance v$ views available with Oracle for the serious Oracle database professional was explored. This chapter will provide further coverage of the inner sanctum of Oracle 11g which is contained in the x$ tables and which form the basis for the dynamic performance v$ views. This chapter will examine:

  • Exploring Oracle 12c new features and internals with the x$ tables

  • Using the x$ tables for Oracle 12c database analysis

  • Scripts using x$ tables with Oracle 12c

Classification of x$ Tables

As one can expect, the structure of the x$ tables is quite cryptic and poorly documented, if at all, within the Oracle literature. What is key is to establish a naming convention for the categories of x$ tables so that the Oracle expert can better understand their meaning and usage. Due to the nature of Oracle database internals, the x$ tables are not documented and their secrets remain internal to Oracle development.

However, there is a useful method to categorize the x$ tables into various functions based on how they operate. Fortunately, in most cases it is quite safe to query the x$ tables without causing any harm. They provide insight into the Oracle database internals for the advanced DBA.

This chapter will provide a useful classification system that can allow the DBA to better understand the nature of x$ tables. At first glance they appear cryptic but are quite easy to decipher once a system has been provided. Yet one needs to review the layers that make up the Oracle 11g database kernel first. Following are the Oracle 11g kernel database layers:

Oracle Kernel Database Layers

KS: Kernel Services

KX: Kernel Execution

K2: Kernel Distributed Transactions

KK: Kernel Compilation

KZ: Kernel Security

KQ: Kernel Query

KA: Kernel Access

KD: Kernel Data

KT: Kernel Transactions

KC: Kernel Cache

KJ: Kernel Locking

KG: Kernel Generic

A short explanation of these kernel layers follows so that one can better understand the relationship between x$ tables and the database kernel for Oracle 11g. The Kernel Services layer gives one the required database services for all other layers in the database kernel stack. For instance, it regulates the initialization parameters in the database for the session and instance levels as well as manages database concurrency operations for locking, latching operations and wait event management for database and instance level statistics. Next to be covered is the Kernel Execution layer.

The Kernel Execution layer performs code executions from the Kernel Compilation layer (KK) and handles bind operations for PL/SQL code as well as recursive calls within the shared pool area for the Oracle 11g SGA.

The Kernel Distributed Transaction(K2) layer manages operations involved within distributed transactions including two-phase commit tasks within the Oracle 11g database.

The Kernel Compilation (KK) layer is responsible for managing the compilation of PL/SQL objects along with tasks performed by the Oracle optimizer.

Next is the Kernel Security layer (KZ) which manages role and system privileges within the Oracle 11g database for security operations.

The Kernel Query (KQ) layer handles row caching operations from the data dictionary. It provides critical tasks so that the Kernel Security (KZ) and Kernel Compilation (KK) layers are able to receive data from the query results performed at this Kernel Query layer.

Kernel Access (KA) provides operations that permit access to database segments as well as routing information to other kernel layers within the Oracle 11g database kernel stack.

Kernel Data(KD) manages the storage layer for segments and data retrieval as well as formatting operations of database segments for storage of table data and index data.

Kernel Transactions (KT) manages freelist operations along with rollback segments including interested transaction list (ITL) allocation for operations that occur within data blocks, undo tasks, and transaction consistency based on the ACID model for relational databases.

Kernel Cache (KC) handles operations around the database buffer cache for Oracle 11g. It works hand-in-hand with system functions to manage shared memory resources including the buffer cache and redo log memory operations.

Kernel Locking (KJ) provides for lock management for RAC environments. It does not manage single instance non-RAC lock operations.

The Kernel Generic layer performs basic database kernel operations.

Following is a brief summary of the different kernel services available for review via the x$ tables. First to be examined are the x$ tables around the Kernel Services (KS) layer for Oracle 11g.

Here is a list of the "important" x$ tables in Oracle 12c:

x$activeckpt

active checkpoint

x$bh

buffer header

x$ckptbuf

checkpoint buffer (queue)

x$dbgalertext

debug alert extented

x$dbglogext

debug log extended

x$dbgricx, x$dbgrifx, x$dbgrikx, x$dbgripx

debug tables

x$dbkece

debug kernel error, critical error

x$dbkefefc

debug kernel error, fatal error flood control

x$dglparam

data guard logical parameters

x$diag_alert_ext

diagnostics alert extended

x$diag_hm_run, x$diag_vhm_run

diagnostics health monitor runs

x$diag_ips_configuration

diagnostics incident packaging service configuration

x$dnfs_meta

dNFS metadata

x$dra_failure

data recovery advisor failures

x$drm_history, x$drm_history_stats

dynamic remastering history, stats

x$jskjobq

job scheduling ?, job queue

x$k2gte,
x$k2gte2

kernel 2-phase commit, global transaction entry

x$kbrpstat

kernel backup recovery process(?) statistics

x$kcbbes

kernel cache, buffer ?

x$kcbbf

kernel cache, buffer buffer_handles

x$kcbfwait

kernel cache, buffer file wait

x$kcbkpfs

kernel cache, buffer ckpt prefetch statistics

x$kcbkwrl

kernel cache, buffer write list

x$kcbldrhist

kernel cache, buffer load direct read history

x$kcbobh

kernel cache, buffer, objectqueue buffer header

x$kcboqh

kernel cache, buffer, object queue header

x$kcbsw

kernel cache, buffer statistics why

x$kcbuwhy

kernel cache, buffer why

x$kcbwbpd

kernel cache, buffer workingset buffer pool descriptor

x$kcbwds

kernel cache, buffer workingset descriptors

x$kcbwh

kernel cache, buffer where/why

x$kcccf

kernel cache, controlfilemanagement control file

x$kcccp

kernel cache, controlfile checkpoint progress

x$kccdi

kernel cache, controlfilemanagement database information

x$kccle

kernel cache, controlfile logfile entry

x$kccnrs, x$kccrsp

kernel cache, controlfile non-guaranteed restorepoint; kernel cache, controlfile restore point

x$kcfis*

kernel cache, file intelligent scan

x$kclcrst

kernel cache, (RAC) lock, consistent read statistics

x$kclfh

kernel cache, (RAC) lock file hashtable

x$kclfi

kernel cache, (RAC) lock file index

x$kclfx

kernel cache, (RAC) lock (element) freelist statistics

x$kcluh

kernel cache, (RAC) lock undo header

x$kclui

kernel cache, (RAC) lock undo index

x$kcmscn

kernel cache, maximum SCN

x$kcrfstrand

kernel cache, redo file strand

x$kcrfx

kernel cache, redo file context

x$kcrrlns

kernel cache, recovery process LNS

x$kdxst

kernel data, index status

x$kdxhs

kernel data, index histogram

x$kewrtb

kernel server (manageability), workload repository tables

x$kfdat

kernel file, disk allocation table?

x$kffxp

kernel file, file extent map

x$kfklib

kernel file, - library

x$kghlu

kernel generic, heap LRUs

x$kglcursor

kernel generic, librarycache cursor

x$kgllk

kernel generic, librarycache lock

x$kglob

kernel generic, librarycache object

x$kglpn

kernel generic, librarycache pin

x$kglrd

kernel generic, librarycache readonly dependency

x$kglst

kernel generic, librarycache statistics

x$kgltr

kernel generic, librarycache translation

x$kgskvft

kernel generic, service, ?? fixed table

x$kjxm

kernel RAC cross-instance (?) messaging

x$kjznhangs, x$kjznhangses

kernel RAC diag node hang session

x$kmgsct

kernel memory, granule scoreboard ?

x$kmgstfr

kernel memory, granule - transfer

x$knstmvr

kernel replication, statistics materialized view refresh

x$kqdpg

kernel query, dictionary PGA

x$kqfco

kernel query, fixed table columns

x$kqfdt

kernel query, fixed derived table

x$kqfp

kernel query, fixed package

x$kqfsz

kernel query, fixed size (size of fixed objects in current version of Oracle)

x$kqfta

kernel query, fixed table

x$kqfvi

kernel query, fixed view

x$kqlfsqce

kernel query, librarycache fixedtable sql cursor environment

x$kqrpd

kernel query, rowcache parent definition

x$kqrsd

kernel query, rowcache subordinate definition

x$krbmsft

kernel recovery, - search file ?

x$krcfh, x$krcfde, x$krcfbh, x$krcbit

kernel recovery, changetracking file, header, descriptor, bitmap header, bitmap block

x$ksbdd

kernel service, background detached (process) definition

x$ksbsrvdt

kernel service, background server detached (process)

x$ksbtabact

kernel service, background - action

x$ksimsi

kernel service, instance management serial (and) instance (numbers)

x$ksipc_info and x$ksipc_proc_stats

kernel service IPC info and process stats

x$ksi_reuse_stats

kernel service, instance, reuse stats

x$ksled, x$kslei, x$ksles

kernel service, lock, event descriptors, events for instance, events for session

x$kslemap

kernel service, lock, event map

x$kslhot

kernel service, lock, hot (blocks)

x$ksllclass

kernel service, lock,, latch class

x$ksllw

kernel service, lock, latch where

x$kslpo

kernel service, latch posting

x$ksmdd

kernel service, memory segmented (array) definition

x$ksmfs

kernel service, memory fixed SGA

x$ksmfsv

kernel service, memory fixed SGA variables

x$ksmhp

kernel service, memory heap

x$ksmjch, x$ksmjs

kernel service, memory, java chunks, java (pool) statistics

x$ksmlru

kernel service, memory LRU

x$ksmls

kernel service, memory large (pool) statistics

x$ksmmem

kernel service, memory

x$ksmns

kernel service, memory numa (pool) statistics

x$ksmpgdst

kernel service, memory PGA detailed statistics

x$ksmpp

kernel service, memory pga heap

x$ksmsp

kernel service, memory sga heap

x$ksmspr

kernel service, memory shared pool reserved

x$ksmsp_dsnew

kernel service, memory shared pool, - statistics new

x$ksmsp_nwex

kernel service, memory shared pool ?

x$ksmss

kernel service, memory sga statistics

x$ksmsst, x$ksmstrs

kernel service, memory, sga streams (pool), streams (pool) statistics

x$ksmssinfo

kernel service, memory sga OS (level) info

x$ksmup

kernel service, memory uga heap

x$ksolsfts

kernel service, object level statistics, fts?

x$ksppcv

kernel service, parameter, current (session) value

x$ksppi

kernel service, parameter, parameter info

x$ksppsv

kernel service, parameter, system value

x$kspspfh

kernel service, parameter spfile header

x$ksrcctx, x$ksrcdes

kernel service, (intra-instance) broadcast, channel context, channel description

x$ksrchdl

kernel service, (intra-instance) broadcast, channel ?

x$kstex

kernel service, trace execution

x$ksulop

kernel service, user long operation

x$ksulv

kernel service, user locale value

x$ksupgp, x$ksupgs

kernel service, user, process group, process group sniped

x$ksupl, x$ksuru

kernel service, user, process (resource) limit, resource usage

x$ksuprlat

kernel service, user process latch

x$ksuse

kernel service, user session

x$ksusecon

kernel service, user session connection

x$ksusm

kernel service, user session migration

x$ksuvmstat

kernel service, user virtual memory statistics

x$kswsastab

kernel service, workgroup services, service table

x$ksxafa

kernel service, execution, - file affinity

x$ksxm_dft

kernel service, execution, modification dml frequency tracking

x$ksxpclient

kernel service, ipc, client

x$ksxpif

kernel service, ipc, interface

x$ksxpping

kernel service, ipc, ping

x$ksxp_stats

kernel service, ipc, stats

x$ktcn*

kernel transaction, change notification *

x$ktcxb

kernel transaction, control, transaction object

x$ktfbfe

kernel tablespace, file bitmap free extent

x$ktfbhc

kernel tablespace, file bitmap header control

x$ktfbnstat

kernel tablespace, file bigfile - stat

x$ktfbue

kernel tablespace, file bitmap used extent

x$ktifb, x$ktiff, x$ktifp, x$ktifv

kernel transaction, in-memory flush, ?

x$ktprhist

kernel transaction, parallel (transaction) recovery history

x$ktsimapool

kernel transaction, - in-memory pool

x$ktsj*

kernel transaction, space job(?)

x$ktskstat

kernel transaction/tablespace, segment shrink statistics

x$ktslchunk

kernel transaction/tablespace, space LOB chunk

x$ktspstat

kernel tablespace, space statistics

x$ktsso

kernel transaction, sort segment

x$ktugd

kernel transaction, undo global data

x$ktuqqry

kernel transaction, undo - query

x$kturhist

kernel transaction, undo recovery history

x$ktusmst

kernel transaction, undo system managed, statistics

x$ktuxe

kernel transaction, undo transaction entry

x$kvii, x$kvit

kernel (performance) view, instance, initialization, transitory (parameters)

x$kwqbpmt

kernel OLTP queue ?

x$kxdbio_stats, x$kxdcm*, x$kxdrs

kernel Exadata, block (level) intelligent operations stats, callback for metrics, resilvering

x$kxfbbox

kernel execution, fast (parallel process) black box

x$kxfpbs

kernel execution, fast (parallel) process batch size

x$kxfpcds, x$kxfpcms, x$kxfpcst

kernel execution, fast (parallel) process, coordinator, dequeue stats, message stats, (query) stats

x$kxfpinstload

kernel execution, fast (parallel) process instance load

x$kxfpsds, x$kxfpsms, x$kxfpsst

kernel execution, fast (parallel) process, slave, dequeue stats, message stats, (query) stats

x$kxsbd

kernel execution, SQL bind data

x$kxttstecs, x$kxttstehs, x$kxttsteis, x$kxttstets

kernel execution, temporary table stats, column stats, histograms, index stats, table stats

x$kywm*

kernel - workload management

x$kzspr, x$kzsro

kernel security, session, privilege, role

x$le

lock element

x$lobsegstat, x$lobstat, x$logstathist

LOB (segment) stats, history

x$logbuf_readhist

Log buffer read histogram

x$messages

(background process) messages

x$modact_length

(sql) module action length (limit)

x$qesmmiwt

query execution, sql memory management ?

x$qesmmsga

query execution, sql memory management ?

x$qksbgses, x$qksbgsys

query compilation service, bug session or system

x$qksceses, x$qkscesys

query compilation service, compilation environment, session or system

x$skgxp_connection, x$skgxp_port

OS kernel generic interface IPC, connections, ports

x$targetrba

target RBA

x$trace

trace

x$uganco

user global area, network connection

x$xplton, x$xpltoo

explain plan sql trace(?) operation name, option

x$xs_sessions

? sessions

x$zasa*

?

 


Also see my notes on Oracle x$ tables:

If you like Oracle tuning, you may enjoy my new book "Oracle Tuning: The Definitive Reference", over 900 pages of BC's favorite tuning tips & scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


 

 

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