A couple of weeks ago I posted a reference list of links to the bug fix notes for several of the most recent versions of Oracle – and several of the links recorded a surprisingly large number of clicks very rapidly, especially the 11.2.0.3 link. As a follow-up on the difficulties of upgrading, then, and with an insight into the number of enhancements and fixes to the optimizer that take place I decided to take a look at recent developments in the “fix control” list, and the “optimizer environment” parameters. Here’s a breakdown of the number of entries in recent versions of Oracle. [Updated for 12.1 and 18.3 May 2019]
v$sys_optimizer_env / x$qkscesys
Version v$ count x$ count 10.2.0.3 25 194 10.2.0.5 25 207 11.1.0.7 41 270 11.2.0.3 49 321 12.1.0.1 55 408 12.2.0.1 64 550 18.3.0.0 66 581 19.11.0.0 69 613
v$system_fix_control / x$qksbgsys
Version count 10.2.0.3 38 10.2.0.5 243 11.1.0.7 229 11.2.0.3 652 12.1.0.1 881 12.2.0.1 1301 18.3.0.0 1391 19.11.0.0 1556
It’s interesting to note the difference between the number of parameters in the v$ and x$ versions of the optimizer environment – and when you see all the hidden parameters in the x$ it may give you some idea of how many things might explain a strange change in execution path on an upgrade. Just for reference, here’s a simple query, with output, from 11.2.0.3:
rem
rem Script: optimizer_env.sql
rem Author: Jonathan Lewis
rem Dated: Feb 2012
rem
set linesize 180
set trimspool on
set pagesize 60
column name format a46
column feature format a24
column value format a15
column def_value format a15
break on feature skip 1
select
FID_QKSCESYROW feature, -- vc64
PNAME_QKSCESYROW name, -- vc50
PVALUE_QKSCESYROW value, -- vc25
DEFPVALUE_QKSCESYROW def_value, -- vc25
KSPNUM_QKSCESYROW parameter, -- number
PNUM_QKSCESYROW opt_param, -- number
FLAGS_QKSCESYROW flags -- number
from
X$QKSCESYS
order by
feature,
name
;
FEATURE NAME VALUE DEF_VALUE PARAMETER OPT_PARAM FLAGS
------------------------ ---------------------------------------- --------------- --------------- ---------- ---------- ----------
QKSFM_ALL _add_stale_mv_to_dependency_list true true 2009 140 6
_bloom_filter_enabled true true 2195 160 7
_bloom_folding_enabled true true 2200 265 7
_bloom_minmax_enabled true true 2387 314 6
_bloom_pruning_enabled true true 2256 211 7
_db_file_optimizer_read_count 8 8 1075 22 6
_direct_path_insert_features 0 0 2298 226 6
_disable_parallel_conventional_load false false 2142 202 6
_dm_max_shared_pool_pct 1 1 2224 163 6
_dml_monitoring_enabled true true 2114 117 6
_enable_dml_lock_escalation false false 2213 159 6
_enable_pmo_ctas 0 0 65535 232 14
_enable_row_shipping true true 2268 215 6
_enable_type_dep_selectivity true true 2023 84 7
_fic_area_size 131072 131072 2117 133 6
_first_k_rows_dynamic_proration true true 2266 207 7
_fix_control_key 0 0 65535 191 14
_force_datefold_trunc false false 2104 111 6
_force_slave_mapping_intra_part_loads false false 2092 192 6
_force_temptables_for_gsets false false 2051 100 6
_force_tmp_segment_loads false false 2091 193 6
_full_pwise_join_enabled true true 2011 79 6
_globalindex_pnum_filter_enabled true true 2211 189 7
_gs_anti_semi_join_allowed true true 2068 103 7
_hash_multiblock_io_count 0 0 1794 21 6
_improved_row_length_enabled true true 2019 82 7
_is_lock_table_for_ddl_wait_lock 0 0 65535 236 14
_kdt_buffering true true 2141 206 6
_left_nested_loops_random true true 2018 81 7
_local_communication_costing_enabled true true 2015 122 7
_local_communication_ratio 50 50 2016 123 6
_minimal_stats_aggregation true true 2045 99 7
_mv_generalized_oj_refresh_opt true true 2333 266 6
_nlj_batching_enabled 1 1 1991 255 7
_optim_new_default_join_sel true true 2073 104 7
_optimizer_adaptive_cursor_sharing true true 1908 225 7
_optimizer_aw_join_push_enabled true true 2285 230 6
_optimizer_aw_stats_enabled true true 2267 210 6
_optimizer_block_size 8192 8192 2163 19 6
_optimizer_cache_stats false false 1912 130 6
_optimizer_connect_by_combine_sw true true 2101 231 7
_optimizer_connect_by_elim_dups true true 2102 283 7
_optimizer_cost_hjsmj_multimatch true true 2227 164 7
_optimizer_enable_extended_stats true true 2297 235 7
_optimizer_extended_cursor_sharing_rel simple simple 1907 224 7
_optimizer_fast_access_pred_analysis true true 2326 278 7
_optimizer_fast_pred_transitivity true true 2325 277 7
_optimizer_ignore_hints false false 2180 146 6
_optimizer_min_cache_blocks 10 10 2244 178 6
_optimizer_mode_force true true 1891 43 7
_optimizer_percent_parallel 101 101 2147 40 6
_optimizer_random_plan 0 0 2181 147 6
_optimizer_rownum_pred_based_fkr true true 2241 175 7
_optimizer_skip_scan_enabled true true 1934 134 7
_optimizer_skip_scan_guess false false 2269 214 6
_optimizer_sortmerge_join_inequality true true 2250 208 7
_optimizer_squ_bottomup true true 1928 132 7
FEATURE NAME VALUE DEF_VALUE PARAMETER OPT_PARAM FLAGS
------------------------ ---------------------------------------- --------------- --------------- ---------- ---------- ----------
QKSFM_ALL _optimizer_system_stats_usage true true 1911 113 7
_optimizer_transitivity_retain true true 2228 165 7
_parallel_broadcast_enabled true true 1939 62 7
_partial_pwise_join_enabled true true 2012 80 6
_partition_view_enabled true true 1900 44 7
_pga_max_size 204800 KB 204800 KB 2054 25 6
_project_view_columns true true 1979 121 6
_px_broadcast_fudge_factor 100 100 1940 63 6
_px_minus_intersect true true 1923 190 7
_px_numa_support_enabled true true 2397 323 6
_px_pwg_enabled true true 2230 166 7
_px_ual_serial_input true true 1922 213 7
_replace_virtual_columns true true 2139 204 7
_result_cache_auto_size_threshold 100 100 1759 252 6
_result_cache_auto_time_threshold 1000 1000 1760 253 6
_right_outer_hash_enable true true 2126 128 7
_row_shipping_explain false false 2264 217 6
_row_shipping_threshold 80 80 2263 216 6
_slave_mapping_enabled true true 2013 125 6
_smm_auto_cost_enabled true true 2058 102 6
_smm_auto_max_io_size 248 KB 248 KB 2057 29 6
_smm_auto_min_io_size 56 KB 56 KB 2056 28 6
_smm_max_size 52428 KB 52428 KB 2062 31 6
_smm_min_size 262 KB 262 KB 2061 30 6
_smm_px_max_size 131072 KB 131072 KB 2063 32 6
_sort_multiblock_read_count 2 2 1863 20 6
_spr_push_pred_refspr true true 2162 129 6
_sql_compatibility 0 0 2370 305 6
_sql_model_unfold_forloops run_time run_time 2212 158 7
_suppress_scn_chk_for_cqn nosuppress_1466 nosuppress_1466 65535 296 14
_table_scan_cost_plus_one true true 2036 93 7
_trace_virtual_columns false false 2138 203 6
_update_bji_ipdml_enabled 0 0 65535 161 14
_virtual_column_overload_allowed true true 2140 205 6
_with_subquery OPTIMIZER OPTIMIZER 2305 242 6
active_instance_count 1 1 65535 12 2
bitmap_merge_area_size 1048576 1048576 1753 15 2
cpu_count 2 2 65535 11 2
db_file_multiblock_read_count 128 128 1073 264 2
dst_upgrade_insert_conv true true 2346 286 2
flashback_table_rpi non_fbt non_fbt 65535 169 10
hash_area_size 131072 131072 1793 14 2
iot_internal_cursor 0 0 65535 293 10
is_recur_flags 0 0 65535 257 2
kkb_drop_empty_segments 0 0 65535 310 10
only_move_row 0 0 65535 315 10
optimizer_mode all_rows all_rows 1890 38 3
optimizer_secure_view_merging true true 2229 167 2
parallel_ddl_mode enabled enabled 65535 37 2
parallel_dml_mode disabled disabled 65535 36 2
parallel_query_mode enabled enabled 65535 35 2
pga_aggregate_target 262144 KB 262144 KB 2052 24 2
result_cache_mode MANUAL MANUAL 1758 212 2
sort_area_retained_size 0 0 1862 17 2
sort_area_size 65536 65536 1861 16 2
total_cpu_count 2 2 65535 275 2
total_processor_group_count 1 1 65535 324 2
FEATURE NAME VALUE DEF_VALUE PARAMETER OPT_PARAM FLAGS
------------------------ ---------------------------------------- --------------- --------------- ---------- ---------- ----------
QKSFM_ALL transaction_isolation_level read_commited read_commited 65535 218 2
workarea_size_policy auto auto 2055 101 2
QKSFM_AQ advanced_queuing_internal_cursor 0 0 65535 287 10
QKSFM_CBO _and_pruning_enabled true true 2365 300 7
_b_tree_bitmap_plans true true 1902 49 7
_cpu_to_io 0 0 1905 33 7
_default_non_equality_sel_check true true 2038 95 6
_disable_datalayer_sampling false false 1986 69 6
_disable_function_based_index false false 2186 150 6
_extended_pruning_enabled true true 2210 154 6
_fast_full_scan_enabled true true 1933 60 7
_gby_hash_aggregation_enabled true true 2209 188 7
_generalized_pruning_enabled true true 2085 109 7
_improved_outerjoin_card true true 2025 85 7
_index_join_enabled true true 2021 83 7
_like_with_bind_as_equality false false 2035 92 6
_nested_loop_fudge 100 100 1978 120 6
_new_initial_join_orders true true 2039 96 7
_new_sort_cost_estimate true true 1913 52 7
_oneside_colstat_for_equijoins true true 2040 97 6
_optim_adjust_for_part_skews true true 2094 110 7
_optim_enhance_nnull_detection true true 1936 61 7
_optim_peek_user_binds true true 2042 98 7
_optimizer_adjust_for_nulls true true 2026 86 6
_optimizer_better_inlist_costing all all 2242 176 7
_optimizer_cartesian_enabled true true 2206 152 6
_optimizer_complex_pred_selectivity true true 2254 186 7
_optimizer_compute_index_stats true true 2095 144 7
_optimizer_connect_by_cb_whr_only false false 2359 295 6
_optimizer_connect_by_cost_based true true 2100 187 7
_optimizer_correct_sq_selectivity true true 2169 149 7
_optimizer_cost_filter_pred false false 2168 135 6
_optimizer_cost_model choose choose 1909 51 7
_optimizer_enable_density_improvements true true 2279 229 7
_optimizer_extended_cursor_sharing udo udo 1906 162 7
_optimizer_extended_stats_usage_control 192 192 2323 260 7
_optimizer_fkr_index_cost_bias 10 10 2308 243 7
_optimizer_improve_selectivity true true 2284 227 7
_optimizer_join_order_control 3 3 2193 151 7
_optimizer_join_sel_sanity_check true true 1935 137 7
_optimizer_max_permutations 2000 2000 1981 23 7
_optimizer_mjc_enabled true true 2127 127 6
_optimizer_new_join_card_computation true true 2077 107 7
_optimizer_or_expansion_subheap true true 2302 249 6
_optimizer_rownum_bind_default 10 10 2280 222 7
_optimizer_search_limit 5 5 2148 10 6
_optimizer_self_induced_cache_cost false false 2243 177 6
_optimizer_sortmerge_join_enabled true true 2128 136 6
_optimizer_star_trans_min_cost 0 0 2303 240 6
_optimizer_star_trans_min_ratio 0 0 2304 241 6
_optimizer_undo_changes false false 2146 118 6
_optimizer_undo_cost_change 11.2.0.3 11.2.0.3 1910 34 7
_optimizer_use_feedback true true 2371 306 7
_optimizer_use_subheap true true 2301 244 6
_ordered_nested_loop true true 1977 64 7
FEATURE NAME VALUE DEF_VALUE PARAMETER OPT_PARAM FLAGS
------------------------ ---------------------------------------- --------------- --------------- ---------- ---------- ----------
QKSFM_CBO _sort_elimination_cost_ratio 0 0 1894 18 6
_system_index_caching 0 0 1984 68 6
_use_column_stats_for_function true true 2028 88 7
cursor_sharing exact exact 1755 48 2
optimizer_capture_sql_plan_baselines false false 2288 238 2
optimizer_dynamic_sampling 2 2 2075 105 3
optimizer_features_enable 11.2.0.3 11.2.0.3 1858 9 2
optimizer_features_hinted 0.0.0 0.0.0 65535 1 10
optimizer_index_caching 0 0 1983 67 2
optimizer_index_cost_adj 100 100 1982 66 2
optimizer_mode_hinted false false 65535 0 10
optimizer_use_pending_statistics false false 2283 228 2
optimizer_use_sql_plan_baselines true true 2289 239 2
parallel_ddl_forced_degree 0 0 65535 5 10
parallel_ddl_forced_instances 0 0 65535 6 10
parallel_dml_forced_dop 0 0 65535 4 10
parallel_execution_enabled true true 65535 2 2
parallel_query_forced_dop 0 0 65535 3 10
parallel_threads_per_cpu 2 2 1954 13 2
skip_unusable_indexes true true 2149 114 3
sqlstat_enabled false false 65535 39 10
statistics_level typical typical 2105 112 2
QKSFM_COMPILATION _allow_level_without_connect_by false false 2179 319 6
_connect_by_use_union_all true true 2103 285 7
QKSFM_CVM _complex_view_merging true true 1914 53 7
QKSFM_DML _dml_frequency_tracking false false 2353 308 6
QKSFM_EXECUTION _aggregation_optimization_settings 0 0 2343 282 7
_deferred_constant_folding_mode DEFAULT DEFAULT 1867 301 6
_rdbms_internal_fplib_enabled false false 1869 263 6
_rowsrc_trace_level 0 0 2240 173 6
cell_offload_compaction ADAPTIVE ADAPTIVE 1879 267 2
cell_offload_plan_display AUTO AUTO 1880 268 2
cell_offload_processing true true 1876 262 2
QKSFM_FBA flashback_data_archive_internal_cursor 0 0 65535 259 10
QKSFM_INDEX optimizer_use_invisible_indexes false false 2322 258 2
QKSFM_JPPD _bloom_predicate_enabled true true 2198 234 6
_optimizer_extend_jppd_view_types true true 2098 157 7
_optimizer_interleave_jppd true true 2307 309 7
_optimizer_multi_level_push_pred true true 2272 220 7
QKSFM_OR_EXPAND _optimizer_or_expansion depth depth 2246 179 7
QKSFM_PARTITION deferred_segment_creation true true 2275 317 2
partition_pruning_internal_cursor 0 0 65535 303 10
QKSFM_PQ _bloom_predicate_pushdown_to_storage true true 2199 269 6
_bloom_pushing_max 512 512 2203 271 6
_bloom_vector_elements 0 0 2197 270 6
_optimizer_degree 0 0 2027 87 6
_optimizer_instance_count 0 0 2331 294 6
FEATURE NAME VALUE DEF_VALUE PARAMETER OPT_PARAM FLAGS
------------------------ ---------------------------------------- --------------- --------------- ---------- ---------- ----------
QKSFM_PQ _parallel_cluster_cache_policy adaptive adaptive 1957 291 6
_parallel_scalability 50 50 2314 292 6
_parallel_syspls_obey_force true true 2315 261 6
_parallel_time_unit 10 10 2311 248 6
_px_partition_scan_enabled true true 2377 311 7
_px_partition_scan_threshold 64 64 2378 312 6
parallel_autodop 0 0 65535 289 2
parallel_ddldml 0 0 65535 290 2
parallel_degree 0 0 65535 246 2
parallel_degree_limit 65535 65535 2312 272 2
parallel_degree_policy manual manual 1945 245 2
parallel_force_local false false 2313 273 2
parallel_hinted none none 65535 304 10
parallel_max_degree 4 4 65535 274 2
parallel_min_time_threshold 10 10 2310 247 2
parallel_query_default_dop 0 0 65535 256 2
QKSFM_STAR_TRANS _optimizer_star_tran_in_with_clause true true 2249 185 7
_optimizer_starplan_enabled true true 2207 153 6
_optimizer_try_st_before_jppd true true 2373 307 7
_optimizer_use_cbqt_star_transformation true true 2362 298 7
star_transformation_enabled false false 1903 50 2
QKSFM_TRANSFORMATION _always_anti_join choose choose 1898 41 7
_always_semi_join choose choose 1976 42 7
_always_star_transformation false false 1901 45 6
_bt_mmv_query_rewrite_enabled true true 2008 139 6
_convert_set_to_join false false 1920 57 7
_cost_equality_semi_join true true 2037 94 7
_dimension_skip_null true true 2252 183 7
_distinct_view_unnesting false false 1925 141 6
_eliminate_common_subexpr true true 1918 55 7
_enable_query_rewrite_on_remote_objs true true 2281 223 6
_force_rewrite_enable false false 2253 184 6
_hash_join_enabled true true 1792 47 6
_max_rwgs_groupings 8192 8192 2010 320 6
_mmv_query_rewrite_enabled true true 2007 138 7
_no_or_expansion false false 1980 65 6
_optimizer_cbqt_factor 50 50 1929 131 6
_optimizer_cbqt_no_size_restriction true true 2234 170 7
_optimizer_coalesce_subqueries true true 2278 276 7
_optimizer_cost_based_transformation linear linear 1927 126 7
_optimizer_dim_subq_join_sel true true 2177 142 7
_optimizer_disable_strans_sanity_checks 0 0 2178 143 6
_optimizer_distinct_agg_transform true true 2342 281 7
_optimizer_distinct_elimination true true 2270 219 7
_optimizer_distinct_placement true true 2277 302 7
_optimizer_eliminate_filtering_join true true 2345 284 7
_optimizer_enable_table_lookup_by_nl true true 2388 316 7
_optimizer_enhanced_filter_push true true 2237 171 7
_optimizer_false_filter_pred_pullup true true 2382 313 7
_optimizer_filter_pred_pullup true true 2099 172 7
_optimizer_filter_pushdown true true 2393 318 6
_optimizer_free_transformation_heap true true 2299 250 6
_optimizer_full_outer_join_to_outer true true 2396 322 7
_optimizer_group_by_placement true true 2276 221 7
_optimizer_join_elimination_enabled true true 2208 168 7
FEATURE NAME VALUE DEF_VALUE PARAMETER OPT_PARAM FLAGS
------------------------ ---------------------------------------- --------------- --------------- ---------- ---------- ----------
QKSFM_TRANSFORMATION _optimizer_join_factorization true true 2360 297 7
_optimizer_native_full_outer_join force force 2296 233 7
_optimizer_nested_rollup_for_gset 100 100 2316 254 6
_optimizer_null_aware_antijoin true true 1899 156 7
_optimizer_order_by_elimination_enabled true true 2248 180 7
_optimizer_outer_join_to_inner true true 2395 321 7
_optimizer_outer_to_anti_enabled true true 2247 181 7
_optimizer_push_down_distinct 0 0 1926 116 7
_optimizer_push_pred_cost_based true true 2097 155 7
_optimizer_reuse_cost_annotations true true 2306 251 6
_optimizer_table_expansion true true 2364 299 7
_optimizer_unnest_all_subqueries true true 1917 288 6
_optimizer_unnest_corr_set_subq true true 2341 280 7
_optimizer_unnest_disjunctive_subq true true 2340 279 7
_or_expand_nvl_predicate true true 2034 91 7
_pivot_implementation_method choose choose 2300 237 7
_pre_rewrite_push_pred true true 2076 106 7
_pred_move_around true true 1919 56 7
_predicate_elimination_enabled true true 1970 119 6
_push_join_predicate true true 1930 58 7
_push_join_union_view true true 1931 59 7
_push_join_union_view2 true true 1932 145 7
_query_cost_rewrite true true 1997 72 6
_query_mmvrewrite_maxcmaps 20 20 2261 198 6
_query_mmvrewrite_maxdmaps 10 10 2260 197 6
_query_mmvrewrite_maxinlists 5 5 2259 196 6
_query_mmvrewrite_maxintervals 5 5 2258 195 6
_query_mmvrewrite_maxpreds 10 10 2257 194 6
_query_mmvrewrite_maxqryinlistvals 500 500 2265 201 6
_query_mmvrewrite_maxregperm 512 512 2262 199 6
_query_rewrite_1 true true 1999 74 6
_query_rewrite_2 true true 1998 73 6
_query_rewrite_drj true true 2004 78 6
_query_rewrite_expression true true 2001 75 6
_query_rewrite_fpc true true 2003 77 6
_query_rewrite_fudge 90 90 2000 8 6
_query_rewrite_jgmigrate true true 2002 76 6
_query_rewrite_maxdisjunct 257 257 2005 27 6
_query_rewrite_or_error false false 1893 46 6
_query_rewrite_setopgrw_enable true true 2184 148 7
_query_rewrite_vop_cleanup true true 2006 124 6
_remove_aggr_subquery true true 1924 115 7
_selfjoin_mv_duplicates true true 2251 182 7
_simple_view_merging true true 1915 174 6
_subquery_pruning_enabled true true 2031 89 7
_subquery_pruning_mv_enabled false false 2032 90 7
_union_rewrite_for_gs yes_gset_mvs yes_gset_mvs 2083 108 7
_unnest_subquery true true 1916 54 7
query_rewrite_enabled true true 1995 70 3
query_rewrite_integrity enforced enforced 1996 71 2
321 rows selected.
There are a few parameters in there which look a little unexpected – why, for example, should deferred_segment_creation affect the optimizer ? One day I might get around to checking how many of these parameters do result in new child cursors being generated if you change them with an alter session or alter system – but it’s not a job I’m going to do in a hurry.
Update (Jan 2022)
Just a quick note that I’ve run the script on an instance of 19.11.0.0 and the number of rows in x$qkscesys is up to 613.
For reference:
- Number of rows in x$ksppi (v$parameter): 5,412
- Number of rows in x$qkscesys (v$sys_optimizer_env): 613
- Difference: 4,799
- Number of rows in parameter list not in optimizer environment: 4,848
- Number of rows in optimizer environment not in parameter list: 49
Oracle Scratchpad 
For ease of use of V$SESSION_FIX_CONTROL I’ve wrote a simple script called bug.sql. Each time I see something unusual related to, say, join elimination, I run @bug elimination and it gives clue what’s next. Or to report what’s new: @bug 11.2.0.3
Comment by Timur Akhmadeev — February 21, 2012 @ 9:36 am GMT Feb 21,2012 |
Here are statistics for my Oracle 11.2.0.2.2:
v$sys_optimizer_env/X$QKSCESYS
Version v$ count x$ count
11.2.0.2(psu2) 49 313
v$system_fix_control / x$qksbgsys
version count
11.2.0.2(psu2) 551
Comment by laimis (lnd) — February 21, 2012 @ 1:53 pm GMT Feb 21,2012 |
Surprisingly honest naming convention for _nested_loop_fudge and _query_rewrite_fudge :)
Comment by Kevin Angus — February 23, 2012 @ 8:34 am GMT Feb 23,2012 |
[…] Jonathan Lewis is taking a look at recent developments in the “fix control” list, and the “optimizer environment” parameters. […]
Pingback by Log Buffer #260, A Carnival of the Vanities for DBAs | The Pythian Blog — February 24, 2012 @ 6:01 am GMT Feb 24,2012 |
That’s a post of real interest. We are in progress of migrating into 11R2.
11.2.0.3 bug list (Doc ID 1348336.1) consists largely of optimizer related bugs. Some of them sound scary:
“13514126 Wrong results due to missing single column range predicate caused by fix to bug 8275054”
Generally, it looks like large number of optimizer improvements resulted into equally large number of serious (wrong results or query crash) bugs.
Comment by laimis (lnd) — February 24, 2012 @ 9:18 am GMT Feb 24,2012 |
[…] 11.2.0.1). This setting acts as an umbrella for all the parameters controlling the optimizer (see this recent post by Jonathan Lewis for more information) including the various bug fix controls that can be seen […]
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[…] version of the same thing – download and install the product, then take a dump of v$system_fix_control – that may also give you some insight into anomalies (that are not necessarily declared as […]
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[…] it. Setting the parameter has the effect of changing the state of a long list of parameters and “fix controls” – but there’s no guarantee that it will reverse out all the code changes between the […]
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