MM-11886: materialize channel search (#9349)

* materialize PublicChannels table

Introduce triggers for each supported database that automatically maintain a subset of the Channels table corresponding to only public channels. This improves corresponding queries that no longer need to filter out 99% DM channels.

This initial commit modifies the channel store directly for easier code reviewing, but the next wraps an experimental version around it to enable a kill switch in case there are unforeseen performance regressions.

This addresses [MM-11886](https://mattermost.atlassian.net/browse/MM-11886) and [MM-11945](https://mattermost.atlassian.net/browse/MM-11945).

* extract the experimental public channels materialization

Wrap the original channel store with an experimental version that
leverages the materialized public channels, but can be disabled to
fallback to the original implementation.

This addresses MM-11947.

* s/ExperimentalPublicChannelsMaterialization/EnablePublicChannelsMaterialization/

* simplify error handling

* move experimental config listener until after store is initialized

1 files changed, 33 insertions, 5 deletions

diff --git a/store/sqlstore/channel_store.go b/store/sqlstore/channel_store.go
index 820fe1e9f..4103980c5 100644
--- a/store/sqlstore/channel_store.go
+++ b/store/sqlstore/channel_store.go
@@ -301,6 +301,21 @@ func (s SqlChannelStore) CreateIndexesIfNotExists() {
 	s.CreateFullTextIndexIfNotExists("idx_channel_search_txt", "Channels", "Name, DisplayName, Purpose")
 }
 
+func (s SqlChannelStore) CreateTriggersIfNotExists() error {
+	// See SqlChannelStoreExperimental
+	return nil
+}
+
+func (s SqlChannelStore) MigratePublicChannels() error {
+	// See SqlChannelStoreExperimental
+	return nil
+}
+
+func (s SqlChannelStore) DropPublicChannels() error {
+	// See SqlChannelStoreExperimental
+	return nil
+}
+
 func (s SqlChannelStore) Save(channel *model.Channel, maxChannelsPerTeam int64) store.StoreChannel {
 	return store.Do(func(result *store.StoreResult) {
 		if channel.DeleteAt != 0 {
@@ -804,12 +819,12 @@ func (s SqlChannelStore) GetTeamChannels(teamId string) store.StoreChannel {
 		_, err := s.GetReplica().Select(data, "SELECT * FROM Channels WHERE TeamId = :TeamId And Type != 'D' ORDER BY DisplayName", map[string]interface{}{"TeamId": teamId})
 
 		if err != nil {
-			result.Err = model.NewAppError("SqlChannelStore.GetChannels", "store.sql_channel.get_channels.get.app_error", nil, "teamId="+teamId+",  err="+err.Error(), http.StatusInternalServerError)
+			result.Err = model.NewAppError("SqlChannelStore.GetTeamChannels", "store.sql_channel.get_channels.get.app_error", nil, "teamId="+teamId+",  err="+err.Error(), http.StatusInternalServerError)
 			return
 		}
 
 		if len(*data) == 0 {
-			result.Err = model.NewAppError("SqlChannelStore.GetChannels", "store.sql_channel.get_channels.not_found.app_error", nil, "teamId="+teamId, http.StatusNotFound)
+			result.Err = model.NewAppError("SqlChannelStore.GetTeamChannels", "store.sql_channel.get_channels.not_found.app_error", nil, "teamId="+teamId, http.StatusNotFound)
 			return
 		}
 
@@ -962,16 +977,16 @@ var CHANNEL_MEMBERS_WITH_SCHEME_SELECT_QUERY = `
 		TeamScheme.DefaultChannelAdminRole TeamSchemeDefaultAdminRole,
 		ChannelScheme.DefaultChannelUserRole ChannelSchemeDefaultUserRole,
 		ChannelScheme.DefaultChannelAdminRole ChannelSchemeDefaultAdminRole
-	FROM 
+	FROM
 		ChannelMembers
-	INNER JOIN 
+	INNER JOIN
 		Channels ON ChannelMembers.ChannelId = Channels.Id
 	LEFT JOIN
 		Schemes ChannelScheme ON Channels.SchemeId = ChannelScheme.Id
 	LEFT JOIN
 		Teams ON Channels.TeamId = Teams.Id
 	LEFT JOIN
-		Schemes TeamScheme ON Teams.SchemeId = TeamScheme.Id 
+		Schemes TeamScheme ON Teams.SchemeId = TeamScheme.Id
 `
 
 func (s SqlChannelStore) SaveMember(member *model.ChannelMember) store.StoreChannel {
@@ -1988,3 +2003,16 @@ func (s SqlChannelStore) ResetLastPostAt() store.StoreChannel {
 		}
 	})
 }
+
+func (s SqlChannelStore) EnableExperimentalPublicChannelsMaterialization() {
+	// See SqlChannelStoreExperimental
+}
+
+func (s SqlChannelStore) DisableExperimentalPublicChannelsMaterialization() {
+	// See SqlChannelStoreExperimental
+}
+
+func (s SqlChannelStore) IsExperimentalPublicChannelsMaterializationEnabled() bool {
+	// See SqlChannelStoreExperimental
+	return false
+}