possible changes in Oracle 20

As this post is written in July 2019, it's highly speculative writing about changes in Oracle version 20.
But at least it's based on some information available from Oracle.

A new autoupgrade.jar version is available at AutoUpgrade Tool (Doc ID 2485457.1). In this Note, there is also a BUGS_20190715.txt which contains (among others):

AUPG-955 Disable NONCDB validation when upgrading a DB to 20c
AUPG-975 upgrade from 12.1.0.2 to 20 is not supported

Based on that I assume, noncdb will not be officially supported anymore, but maybe it's not supported in the autoupgrade.jar, but manual steps are still allowed & supported - we will se.
Also a direct upgrade from 12.1 to 20 is out of scope of this tool.

But there is more information available.
in the autoupgrade.jar in directory resources/preupgrade/config/ there is a file parameters20.properties. It contains information about deprecated/obsolete/removed parameters.

The changes in comparison to 19 I found:

from deprecated to removed:
unified_audit_sga_queue_size

from deprecated to obsolete:
cluster_database_instances

new parameters and their status:

PARAMETER	STATUS
_arch_sim_mode	removed
_gc_async_receive	removed
_hcs_disable_sp_jback_opt	removed
_autonomous_performance_features_index	removed
_cgs_os_level_connection_reqno	deprecated
_autonomous_performance_features_stats	removed
_px_monitor_load	obsolete
_hcs_disable_level_prune_vis_lvs	removed
_hcs_disable_level_prune_gby	removed
_asm_enable_parity_datafile_creation	removed
_part_access_version_by_number	obsolete
_tablespace_encryption_default_algorithm	removed
_hcs_disable_cell_qry_meas_prune_opt	removed
_unified_audit_flush_threshold	removed
_optimizer_stats_on_conventional_dml_config	removed
_reset_maxcap_history	removed
_ldr_io_size2	obsolete
_hang_long_wait_time_threshold	removed
_read_mostly_instance	deprecated
_cgs_os_level_connection_pthreadno	removed
_max_cr_rollbacks	deprecated
_hcs_enable_multi_parent_gen	removed
_disable_thread_snapshot	removed
_hcs_disable_tgt_depths_opt	removed
_enable_imc_mira	removed
_log_archive_avoid_memcpy	removed
_gcs_min_slaves	deprecated
_hcs_enable_dynamic_cache	removed
_unified_audit_flush_interval	removed
_hcs_disable_hord_in_oby_prune	removed
_ta_lns_wait_for_arch_log	removed
_hcs_disable_jback_opt_for_hord_in_oby	removed
_show_mgd_recovery_state	removed
_hcs_disable_pushed_preds_in_gen_sql	removed
_hcs_disable_cell_qry_tmpls	removed
_test_param_5	deprecated
_autonomous_performance_features	removed
_session_percent_threshold	removed
_ash_compression_enable	deprecated
_kebm_max_parallel_intensive_autotasks	removed

let's see if this will change in next iterations.

The biggest value of such sources (for me) is the reliability. It's not something a vendor wants the customers to know/act on (like a "what changed" document would be); it's the information required by tools, so no political filters are there.