前回に続き、Oracle Database19cと21cの隠しパラメータを比較した結果の纏め。今回はデフォルト値や設定範囲(ALTER SESSION/SYSTEM可否)、名称変更されたと思われる隠しパラメータを記載する。
2.デフォルト値が変わった隠しパラメータ
19cと21cでデフォルトが変更となった隠しパラメータは下記の61個。
| パラメータ名 | デフォルト値(19c) | デフォルト値(21c) | パラメータ概要 |
|---|---|---|---|
| _active_instance_count | 1024 | number of active instances in the cluster database | |
| _ash_compression_enable | TRUE | FALSE | To enable or disable string compression in ASH |
| _asm_enable_lostwrite_scrub | FALSE | TRUE | Allow lost write detection in scrubbing |
| _awr_warehouse_enabled | FALSE | TRUE | Enable/Disable AWR warehouse functionality |
| _bct_buffer_allocation_max | 104857600 | 1073741824 | maximum size of all change tracking buffer allocations, in bytes |
| _bct_mrp_timeout | 600 | 5 | CTWR MRP wait timeout (seconds), zero to wait forever |
| _cgs_combine_css_events | 7 | 31 | CGS registration flags for CSS event combining |
| _cgs_publish_netinfo_collect_event_chm | rcfg-half-timeout,rcfg-timeout,rcfg-done,idleconn-half-timeout,idleconn-timeout-imr,idleconn-cln | rcfg-half-timeout,rcfg-timeout,rcfg-done,idleconn-half-timeout,idleconn-timeout-imr,idleconn-cln,rcfg-begin,rcfg-pngchkdone,rcfg-memchg | enable cgs publish collect_netinfo event to event stream for CHM |
| _check_block_after_checksum | TRUE | FALSE | perform block check after checksum if both are turned on |
| _controlfile_split_brain_check | TRUE | FALSE | Check for a split-brain in distributed lock manager domain |
| _cp_num_hash_latches | 1 | connection pool number of hash latches | |
| _cpu_util_adj_force | 0 | 1 | force cpu util adjustment |
| _db_flash_cache_max_read_retry | 3 | 10 | Flash cache max read retry |
| _db_minimum_auxsize_percent | 10 | 0 | min percent of aux buffers to be maintained before using aux2 |
| _db_num_evict_waitevents | 64 | 16384 | number of evict wait events |
| _db_xmem_hot_switch_criteria | 4 | 195 | Xmem buffer touch count which makes this buffer candidate of switching to DRAM buffer |
| _dbfs_symlink_path_prefix | FALSE | TRUE | allow or disallow symlink creation in dbfs outside path_prefix |
| _disable_oradebug_commands | none | restricted | disable execution of certain categories of oradebug commands |
| _dm_max_shared_pool_pct | 1 | 5 | max percentage of the shared pool to use for a mining model |
| _enable_dbwr_auto_tracing | 0 | 1 | enable dbwriter auto-tracing |
| _enable_nvm_dispatcher | FALSE | 0 | Enable NVM Dispatcher |
| _enable_pluggable_database | FALSE | TRUE | Enable Pluggable Database |
| _enable_replay_upgrade_diag | FALSE | TRUE | Enable diagnostics for Replay Upgrade |
| _enable_tcpinfo_statistics | 111 | 238 | Enable TCP Info Statistics |
| _federation_max_root_clones | 5 | 4000 | Maximum number of Federation Root Clones per Application |
| _fg_fast_sync_spin_usecs | 300 | 100 | DAX log file sync spin time |
| _gc_max_downcvt | 2048 | 0 | maximum downconverts to process at one time |
| _gc_save_cleanout | TRUE | FALSE | if TRUE, save cleanout to apply later |
| _gc_spin_time | 16 | 0 | rdma spin time |
| _gcr_cpu_min_hard_limit | 2560 | 0 | hard limit for min free CPU to flag high CPU |
| _gcr_enable_new_drm_check | FALSE | TRUE | if FALSE, revert to old drm load metric |
| _gcs_partial_open_mode | 0 | 1 | partial open cache fusion service in reconfiguration |
| _ges_freeable_res_chunk_free | FALSE | TRUE | if TRUE, free dynamic resource chunks which are freeable |
| _hang_allow_resolution_on_single_nonrac | FALSE | DBRM | Hang Management allow resolution on single non-RAC instances |
| _hang_blocked_session_percent_threshold | 0 | 20 | Hang Manager fast-track blocked session percent threshold |
| _high_priority_processes | LMS*|LM1*|LM2*|LM3*|LM4*|LM5*|LM6*|LM7*|LM8*|LM9* | LGWR|LMS*|LM1*|LM2*|LM3*|LM4*|LM5*|LM6*|LM7*|LM8*|LM9* | High Priority Process Name Mask |
| _highthreshold_undoretention | 4294967294 | 31536000 | high threshold undo_retention in seconds |
| _inmemory_dynamic_scan_disable_threshold | 10 | 20 | Inmemory dynamic scan disable threshold |
| _inmemory_hwm_expansion | 0 | 1 | If 0, the highwatermark CU is dropped when expanded |
| _inmemory_memprot | TRUE | FALSE | enable or disable memory protection for in-memory |
| _ka_locks_per_sector | 4 | 12 | locks per sector in kernel accelerator |
| _kdli_allow_corrupt | TRUE | FALSE | allow corrupt filesystem_logging data blocks during read/write |
| _ksws_java_patching | 999 | 0 | java patching mode |
| _kttext_warning | 5 | 1285 | tablespace pre-extension warning threshold in percentage |
| _lm_comm_tkts_calc_period_length | 1000 | 100000 | Weighted average calculation interval length (us) |
| _lm_hash_control | 1 | 5 | bit field controlling the hashing behavior of the lock manager |
| _nls_binary | FALSE | TRUE | force binary collation |
| _optimizer_gather_stats_on_conventional_dml | TRUE | FALSE | optimizer online stats gathering for conventional DML |
| _optimizer_key_vector_payload_dim_aggs | FALSE | TRUE | enables or disables dimension payloading of aggregates in VT |
| _optimizer_undo_cost_change | 19.1.0 | 21.1.0 | optimizer undo cost change |
| _optimizer_use_stats_on_conventional_dml | TRUE | FALSE | use optimizer statistics gathered for conventional DML |
| _pga_limit_time_until_killed | 15 | 30 | seconds to wait before killing session over limit |
| _reconfiguration_opt_level | 109 | 237 | reconfiguration optimization level |
| _result_cache_block_size | 1024 | 4096 | result cache block size |
| _result_cache_timeout | 10 | 1 | maximum time (sec) a session waits for a result |
| _session_prediction_failover_buffer | 0 | 1 | session prediction failover buffer |
| _size_of_log_table | 30 | 100 | modifying this hidden parameter, will modify the sizeof the v$gcr_log table |
| _sqlexec_hash_based_distagg_enabled | FALSE | TRUE | enable hash based distinct aggregation for gby queries |
| _sqlmon_max_planlines | 300 | 1000 | Number of plan lines beyond which a plan cannot be monitored |
| _standby_implicit_rcv_timeout | 1 | 3 | minutes to wait for redo during standby implicit recovery |
| _tsenc_obfuscate_key | both | none | Encryption key obfuscation in memory |
3.設定可能範囲に変更があったパラメータ
ALTER SESSIONやALTER SYSTEMでの変更可否に関して差分のあった隠しパラメータは以下の通り。大半は21cでは(動的)変更可能になったものが多い。
| パラメータ名 | 21cでの変更内容 | パラメータ概要 |
|---|---|---|
| _auto_manage_exadata_disks | SESSION/SYSTEM単位で変更可になった | Automate Exadata disk management |
| _cdb_port | SYSTEM単位で変更可になった | Port number for CDB |
| _column_level_stats | SESSION単位で変更不可になった | Turn column statistics collection on or off |
| _enable_tcpinfo_statistics | SESSION/SYSTEM単位で変更可になった | Enable TCP Info Statistics |
| _kgl_time_to_wait_for_locks | SESSION/SYSTEM単位で変更可になった | time to wait for locks and pins before timing out |
| _kse_snap_ring_size | SYSTEM単位で変更不可になった | ring buffer to debug internal error 17090 |
| _lm_tickets | SYSTEM単位で変更可になった | GES messaging tickets |
4.隠しパラメータ名に変更があったパラメータ
実は他にもあるかもしれないが、デフォルト値や設定範囲などは同じなのに、パラメータ名の一部だけが変更された様に見えるパラメータが2つあったので、記載しておく。
| パラメータ名(19c) | パラメータ名(21c) | パラメータ概要(19c) | パラメータ概要(21c) |
|---|---|---|---|
| _connect_string_params_after_logon_triggers | _connect_string_settings_after_logon_triggers | set connect string session parameters after logon triggers | set connect string session settings after logon triggers |
| _connect_string_params_unalterable | _connect_string_settings_unalterable | make connect string session parameters unalterable | make connect string session settings unalterable |
新規登場した隠しパラメータは次回に。
