[docs] Add db migration tip for slow hardware instances. (#4457)

This PR adds a new section to the documentation to contain workarounds for running
GtS on slow hardware. Right now it only contains a procedure on how to run migrations
on a different database instance in case the original database is too slow to finish
a database migration in a timely manner.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4457
Co-authored-by: Daniël Franke <df@ponc.tech>
Co-committed-by: Daniël Franke <df@ponc.tech>

docs/admin/slow_hardware.md

@@ -0,0 +1,43 @@
+# Managing GtS on slow hardware
+
+While GoToSocial runs great on lower-end hardware, some operations are not practical on it, especially
+instances with the database on slow storage (think anything that is not an SSD).  This document
+offers some suggestions on how to work around common issues when running GtS on slow hardware.
+
+## Running database migrations on a different machine
+
+Sometimes a database migration will need to do operations that are taxing on the database's storage.
+These operations can take days if the database resides on a hard disk or SD card. If your
+database is on slow storage, it can save a lot of time to follow the following procedure:
+
+!!! danger
+
+    It might seem tempting to keep GtS running while you run the migrations on another machine, but
+    doing this will lead to all the posts that are received during the migration post disappearing
+    once the migrated database is re-imported.
+
+ 1. Shut down GtS
+ 2. Take a [backup](backup_and_restore.md#what-to-backup-database) of the database
+ 3. Import the database on faster hardware
+ 4. Run the GtS migration on the faster hardware
+ 5. Take a backup of the resultant database
+ 6. Import the resultant backup and overwrite the old database
+ 7. Start GtS with the new version
+
+### Running GtS migrations separately
+
+After you import the database on the faster hardware, you can run the migration without starting
+GtS by downloading the *target* GtS version from the [releases](https://codeberg.org/superseriousbusiness/gotosocial/releases) page.
+For instance, if you are running `v0.19.2` and you want to upgrade to `v0.20.0-rc1`, download the
+latter version. Once you have the binary, set it to executable by running `chmod u+x /path/to/gotosocial`. Afterwards, copy the configuration of the original server, and alter
+it with the location of the new database. We copy the configuration in case variables like
+the hostname is used in the migration, we want to keep that consistent.
+Once everything is in place, you can run the migration like this:
+
+```sh
+$ /path/to/gotosocial --config-path /path/to/config migrations run
+```
+
+This will run all the migrations, just like GtS would if it was started normally. Once this is done
+you can copy the result to the original instance and start the new GtS version there as well, which
+will see that everything is migrated and that there's nothing to do except run as expected.

internal/federation/dereferencing/status.go

@@ -608,6 +608,9 @@ func (d *Dereferencer) enrichStatus(
 		return nil, nil, gtserror.Newf("error populating emojis for status %s: %w", uri, err)
 	}
 
+	// Check if interaction policy has changed between status and latestStatus.
+	interactionPolicyChanged := status.InteractionPolicy.DifferentFrom(latestStatus.InteractionPolicy)
+
 	if isNew {
 		// Simplest case, insert this new remote status into the database.
 		if err := d.state.DB.PutStatus(ctx, latestStatus); err != nil {
@@ -625,6 +628,7 @@ func (d *Dereferencer) enrichStatus(
 			tagsChanged,
 			mediaChanged,
 			emojiChanged,
+			interactionPolicyChanged,
 		)
 		if err != nil {
 			return nil, nil, gtserror.Newf("error handling edit for status %s: %w", uri, err)
@@ -1057,6 +1061,7 @@ func (d *Dereferencer) handleStatusEdit(
 	tagsChanged bool,
 	mediaChanged bool,
 	emojiChanged bool,
+	interactionPolicyChanged bool,
 ) (
 	cols []string,
 	err error,
@@ -1141,6 +1146,15 @@ func (d *Dereferencer) handleStatusEdit(
 		// been previously populated properly.
 	}
 
+	if interactionPolicyChanged {
+		// Interaction policy changed.
+		cols = append(cols, "interaction_policy")
+
+		// Int pol changed doesn't necessarily
+		// indicate an edit, it may just not have
+		// been previously populated properly.
+	}
+
 	if edited {
 		// Get previous-most-recent modified time,
 		// which will be this edit's creation time.

internal/gtsmodel/interactionpolicy.go

@@ -17,6 +17,8 @@
 
 package gtsmodel
 
+import "slices"
+
 // A policy URI is GoToSocial's internal representation of
 // one ActivityPub URI for an Actor or a Collection of Actors,
 // specific to the domain of enforcing interaction policies.
@@ -232,6 +234,39 @@ type PolicyRules struct {
 	ManualApproval PolicyValues `json:"WithApproval,omitempty"`
 }
 
+// DifferentFrom returns true if pr1 and pr2
+// are not equal in terms of nilness or content.
+func (pr1 *PolicyRules) DifferentFrom(pr2 *PolicyRules) bool {
+	// If one PolicyRules is nil and
+	// the other isn't, they're different.
+	if pr1 == nil && pr2 != nil ||
+		pr1 != nil && pr2 == nil {
+		return true
+	}
+
+	// Check if AutomaticApproval
+	// differs between the two.
+	if slices.Compare(
+		pr1.AutomaticApproval,
+		pr2.AutomaticApproval,
+	) != 0 {
+		return true
+	}
+
+	// Check if ManualApproval
+	// differs between the two.
+	if slices.Compare(
+		pr1.ManualApproval,
+		pr2.ManualApproval,
+	) != 0 {
+		return true
+	}
+
+	// They're the
+	// same picture.
+	return false
+}
+
 // Returns the default interaction policy
 // for the given visibility level.
 func DefaultInteractionPolicyFor(v Visibility) *InteractionPolicy {
@@ -422,3 +457,41 @@ func DefaultInteractionPolicyDirect() *InteractionPolicy {
 	*c = *defaultPolicyDirect
 	return c
 }
+
+// DifferentFrom returns true if p1 and p2 are different.
+func (ip1 *InteractionPolicy) DifferentFrom(ip2 *InteractionPolicy) bool {
+	// If one policy is null and the
+	// other isn't, they're different.
+	if ip1 == nil && ip2 != nil ||
+		ip1 != nil && ip2 == nil {
+		return true
+	}
+
+	// If they're both nil we don't
+	// need to check anything else.
+	if ip1 == nil && ip2 == nil {
+		return false
+	}
+
+	// If CanLike differs from one policy
+	// to the next, they're different.
+	if ip1.CanLike.DifferentFrom(ip2.CanLike) {
+		return true
+	}
+
+	// If CanReply differs from one policy
+	// to the next, they're different.
+	if ip1.CanReply.DifferentFrom(ip2.CanReply) {
+		return true
+	}
+
+	// If CanAnnounce differs from one policy
+	// to the next, they're different.
+	if ip1.CanAnnounce.DifferentFrom(ip2.CanAnnounce) {
+		return true
+	}
+
+	// Looks the
+	// same chief.
+	return false
+}

mkdocs.yml

@@ -38,7 +38,7 @@ plugins:
 extra:
   alternate:
     - name: English
-      link: /en/ 
+      link: /en/
       lang: en
     - name: 中文
       link: /zh-cn/
@@ -149,6 +149,7 @@ nav:
       - "admin/spam.md"
       - "admin/database_maintenance.md"
       - "admin/themes.md"
+      - "admin/slow_hardware.md"
   - "Federation":
       - "federation/index.md"
       - "federation/http_signatures.md"