Manual:Suitability of tables for sharing

From mediawiki.org

Some tables lend themselves better than others to being shared using $wgSharedTables .

Table Can be shared? Comments
archive No ar_rev_id collisions
category No cat_title collisions
categorylinks No cl_from collisions
change_tag No ct_log_id collisions
comment No Houses comments linked to multiple unshareable tables.
externallinks No el_from collisions
filearchive No ?
image No To have a shared media repository, see $wgForeignFileRepos
imagelinks No il_from collisions
interwiki Yes The interwiki table contains mostly static data; it may be useful to share if you have many custom interwikis.
ipblocks Yes By sharing the ipblocks table, you can have "global blocks" so that a block on one wiki will block the user or IP on all other wikis using the shared database. There can be some minor issues when sharing the ipblocks table. Viz., the ipb_reason field is set as the "reason" on Special:Block when blocking a user. When a blocked user sees the "You are blocked" message, this is parsed as wikitext, and links are parsed on Special:BlockList, you will need to make sure when blocking a user that the message makes sense on all wikis. Also, block logs will not be shared. (You must also share your user table for shared ipblocks to work.)

Note that the comment table cannot be shared, which may cause issues with some blocking-related code, per phab:T214011.

iwlinks No iwl_from collisions
job No job_title collisions
l10n_cache ? ?
langlinks No ll_from collisions
linktarget ? ?
logging No log_page collisions
log_search No ls_value collisions
module_deps ? ?
objectcache Yes ?
oldimage ? ?
page No page_namespace and page_title collisions
pagelinks No pl_from collisions
page_props No pp_page collisions
page_restrictions No pr_page collisions
protected_titles No pt_namespace and pt_title collisions
querycache No qc_namespace and qc_title collisions
querycachetwo No qcc_namespace and qcc_title collisions
querycache_info No qc_type collisions
recentchanges No rc_cur_id collisions
redirect No rd_from collisions
revision No rev_page collisions
searchindex No si_page collisions
site_stats Yes The site_stats table could possibly be shared, to aggregate data over all your wikis.
tag_summary No ts_rc_id , ts_log_id , and ts_rev_id collisions
templatelinks No tl_from , tl_namespace and tl_title collisions
transcache ? ?
updatelog ? ?
uploadstash ? ?
user Yes A shared user table can be used to have multiple wikis that have shared user registrations, so that users need only sign up to one wiki. See Manual:Shared database .
user_former groups Yes You would need to share the user table as well, and presumably user_groups.
user_groups Yes Sharing the user_groups table will allow you to have global user groups. As with the block log, the user rights log is not shared.
user_newtalk ? ?
user_properties Yes By default, the user_properties table is included in the list of shared tables.
valid_tag ? ?
watchlist No wl_namespace and wl_title collisions