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

store/storetest/mocks/ChannelStore.go

@@ -130,6 +130,30 @@ func (_m *ChannelStore) Delete(channelId string, time int64) store.StoreChannel
 	return r0
 }
 
+// DisableExperimentalPublicChannelsMaterialization provides a mock function with given fields:
+func (_m *ChannelStore) DisableExperimentalPublicChannelsMaterialization() {
+	_m.Called()
+}
+
+// DropPublicChannels provides a mock function with given fields:
+func (_m *ChannelStore) DropPublicChannels() error {
+	ret := _m.Called()
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func() error); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
+// EnableExperimentalPublicChannelsMaterialization provides a mock function with given fields:
+func (_m *ChannelStore) EnableExperimentalPublicChannelsMaterialization() {
+	_m.Called()
+}
+
 // Get provides a mock function with given fields: id, allowFromCache
 func (_m *ChannelStore) Get(id string, allowFromCache bool) store.StoreChannel {
 	ret := _m.Called(id, allowFromCache)
@@ -601,6 +625,20 @@ func (_m *ChannelStore) InvalidateMemberCount(channelId string) {
 	_m.Called(channelId)
 }
 
+// IsExperimentalPublicChannelsMaterializationEnabled provides a mock function with given fields:
+func (_m *ChannelStore) IsExperimentalPublicChannelsMaterializationEnabled() bool {
+	ret := _m.Called()
+
+	var r0 bool
+	if rf, ok := ret.Get(0).(func() bool); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Get(0).(bool)
+	}
+
+	return r0
+}
+
 // IsUserInChannelUseCache provides a mock function with given fields: userId, channelId
 func (_m *ChannelStore) IsUserInChannelUseCache(userId string, channelId string) bool {
 	ret := _m.Called(userId, channelId)
@@ -631,6 +669,20 @@ func (_m *ChannelStore) MigrateChannelMembers(fromChannelId string, fromUserId s
 	return r0
 }
 
+// MigratePublicChannels provides a mock function with given fields:
+func (_m *ChannelStore) MigratePublicChannels() error {
+	ret := _m.Called()
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func() error); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
 // PermanentDelete provides a mock function with given fields: channelId
 func (_m *ChannelStore) PermanentDelete(channelId string) store.StoreChannel {
 	ret := _m.Called(channelId)

store/storetest/mocks/SqlStore.go

@@ -241,6 +241,20 @@ func (_m *SqlStore) DoesTableExist(tablename string) bool {
 	return r0
 }
 
+// DoesTriggerExist provides a mock function with given fields: triggerName
+func (_m *SqlStore) DoesTriggerExist(triggerName string) bool {
+	ret := _m.Called(triggerName)
+
+	var r0 bool
+	if rf, ok := ret.Get(0).(func(string) bool); ok {
+		r0 = rf(triggerName)
+	} else {
+		r0 = ret.Get(0).(bool)
+	}
+
+	return r0
+}
+
 // DriverName provides a mock function with given fields:
 func (_m *SqlStore) DriverName() string {
 	ret := _m.Called()

store/storetest/mocks/SqlSupplier.go

@@ -0,0 +1,29 @@
+// Code generated by mockery v1.0.0. DO NOT EDIT.
+
+// Regenerate this file using `make store-mocks`.
+
+package mocks
+
+import gorp "github.com/mattermost/gorp"
+import mock "github.com/stretchr/testify/mock"
+
+// SqlSupplier is an autogenerated mock type for the SqlSupplier type
+type SqlSupplier struct {
+	mock.Mock
+}
+
+// GetMaster provides a mock function with given fields:
+func (_m *SqlSupplier) GetMaster() *gorp.DbMap {
+	ret := _m.Called()
+
+	var r0 *gorp.DbMap
+	if rf, ok := ret.Get(0).(func() *gorp.DbMap); ok {
+		r0 = rf()
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(*gorp.DbMap)
+		}
+	}
+
+	return r0
+}