| // Copyright (C) 2016 The Android Open Source Project |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| package com.google.gerrit.server.notedb; |
| |
| import com.google.gerrit.server.notedb.NoteDbChangeState.PrimaryStorage; |
| |
| /** |
| * Holds the current state of the NoteDb migration. |
| * |
| * <p>The migration will proceed one root entity type at a time. A <em>root entity</em> is an entity |
| * stored in ReviewDb whose key's {@code getParentKey()} method returns null. For an example of the |
| * entity hierarchy rooted at Change, see the diagram in {@code |
| * com.google.gerrit.reviewdb.client.Change}. |
| * |
| * <p>During a transitional period, each root entity group from ReviewDb may be either <em>written |
| * to</em> or <em>both written to and read from</em> NoteDb. |
| * |
| * <p>This class controls the state of the migration according to options in {@code gerrit.config}. |
| * In general, any changes to these options should only be made by adventurous administrators, who |
| * know what they're doing, on non-production data, for the purposes of testing the NoteDb |
| * implementation. Changing options quite likely requires re-running {@code RebuildNoteDb}. For |
| * these reasons, the options remain undocumented. |
| */ |
| public abstract class NotesMigration { |
| /** |
| * Read changes from NoteDb. |
| * |
| * <p>Change data is read from NoteDb refs, but ReviewDb is still the source of truth. If the |
| * loader determines NoteDb is out of date, the change data in NoteDb will be transparently |
| * rebuilt. This means that some code paths that look read-only may in fact attempt to write. |
| * |
| * <p>If true and {@code writeChanges() = false}, changes can still be read from NoteDb, but any |
| * attempts to write will generate an error. |
| */ |
| public abstract boolean readChanges(); |
| |
| /** |
| * Write changes to NoteDb. |
| * |
| * <p>Updates to change data are written to NoteDb refs, but ReviewDb is still the source of |
| * truth. Change data will not be written unless the NoteDb refs are already up to date, and the |
| * write path will attempt to rebuild the change if not. |
| * |
| * <p>If false, the behavior when attempting to write depends on {@code readChanges()}. If {@code |
| * readChanges() = false}, writes to NoteDb are simply ignored; if {@code true}, any attempts to |
| * write will generate an error. |
| */ |
| protected abstract boolean writeChanges(); |
| |
| /** |
| * Read sequential change ID numbers from NoteDb. |
| * |
| * <p>If true, change IDs are read from {@code refs/sequences/changes} in All-Projects. If false, |
| * change IDs are read from ReviewDb's native sequences. |
| */ |
| public abstract boolean readChangeSequence(); |
| |
| /** @return default primary storage for new changes. */ |
| public abstract PrimaryStorage changePrimaryStorage(); |
| |
| /** |
| * Disable ReviewDb access for changes. |
| * |
| * <p>When set, ReviewDb operations involving the Changes table become no-ops. Lookups return no |
| * results; updates do nothing, as does opening, committing, or rolling back a transaction on the |
| * Changes table. |
| */ |
| public abstract boolean disableChangeReviewDb(); |
| |
| /** |
| * Whether to fail when reading any data from NoteDb. |
| * |
| * <p>Used in conjunction with {@link #readChanges()} for tests. |
| */ |
| public boolean failOnLoad() { |
| return false; |
| } |
| |
| public boolean commitChangeWrites() { |
| // It may seem odd that readChanges() without writeChanges() means we should |
| // attempt to commit writes. However, this method is used by callers to know |
| // whether or not they should short-circuit and skip attempting to read or |
| // write NoteDb refs. |
| // |
| // It is possible for commitChangeWrites() to return true and |
| // failChangeWrites() to also return true, causing an error later in the |
| // same codepath. This specific condition is used by the auto-rebuilding |
| // path to rebuild a change and stage the results, but not commit them due |
| // to failChangeWrites(). |
| return writeChanges() || readChanges(); |
| } |
| |
| public boolean failChangeWrites() { |
| return !writeChanges() && readChanges(); |
| } |
| |
| public boolean enabled() { |
| return writeChanges() || readChanges(); |
| } |
| } |