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feat(graphcache): Remove refLock and add dirtyKeys / skip GC runs in …
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…unsettled state

This skips GC runs when we previously would've used `refLock` to skip over
entities that are "locked" by optimistic and deferred layers. Instead, we
now simply skip GC runs when `optimisticOrder` is non-empty, meaning that
we simply forgo garbage collection runs when we know it's unlikely we'll
need them.
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@kitten
kitten committed Dec 7, 2022
1 parent ece64fc commit e359593
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Showing 3 changed files with 59 additions and 100 deletions.
5 changes: 5 additions & 0 deletions .changeset/orange-squids-care.md
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@@ -0,0 +1,5 @@
---
'@urql/exchange-graphcache': patch
---

Add skipping of garbage collection runs when the cache is waiting for optimistic, deferred or other results in layers. This means that we only take an opportunity to run garbage collection after results have settled and are hence decreasing the chance of hogging the event loop when a run isn't needed.
2 changes: 1 addition & 1 deletion exchanges/graphcache/src/store/data.test.ts
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Expand Up @@ -87,7 +87,7 @@ describe('garbage collection', () => {
InMemoryData.reserveLayer(data, 1);
InMemoryData.gc();

expect(InMemoryData.readRecord('Todo:1', 'id')).toBe(undefined);
expect(InMemoryData.readRecord('Todo:1', 'id')).toBe('1');
expect(InMemoryData.getCurrentDependencies()).toEqual(
new Set(['Query.todo', 'Todo:1'])
);
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152 changes: 53 additions & 99 deletions exchanges/graphcache/src/store/data.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -41,8 +41,6 @@ export interface InMemoryData {
queryRootKey: string;
/** Number of references to each entity (except "Query") */
refCount: KeyMap<number>;
/** Number of references to each entity on optimistic layers */
refLock: OperationMap<KeyMap<number>>;
/** A map of entity fields (key-value entries per entity) */
records: NodeMap<EntityField>;
/** A map of entity links which are connections from one entity to another (key-value entries per entity) */
Expand All @@ -51,6 +49,8 @@ export interface InMemoryData {
deferredKeys: Set<number>;
/** A set of Query operation keys that are in-flight and awaiting a result */
commutativeKeys: Set<number>;
/** A set of Query operation keys that have been written to */
dirtyKeys: Set<number>;
/** The order of optimistic layers */
optimisticOrder: number[];
/** This may be a persistence adapter that will receive changes in a batch */
Expand Down Expand Up @@ -160,7 +160,7 @@ export const clearDataState = () => {
let i = data.optimisticOrder.length;
while (
--i >= 0 &&
data.refLock.has(data.optimisticOrder[i]) &&
data.dirtyKeys.has(data.optimisticOrder[i]) &&
data.commutativeKeys.has(data.optimisticOrder[i])
)
squashLayer(data.optimisticOrder[i]);
Expand All @@ -175,16 +175,19 @@ export const clearDataState = () => {
currentDebugStack.length = 0;
}

// Schedule deferred tasks if we haven't already
if (process.env.NODE_ENV !== 'test' && !data.defer) {
data.defer = true;
setTimeout(() => {
initDataState('read', data, null);
gc();
persistData();
clearDataState();
data.defer = false;
});
if (process.env.NODE_ENV !== 'test') {
// Schedule deferred tasks if we haven't already, and if either a persist or GC run
// are likely to be needed
if (!data.defer && (data.storage || !data.optimisticOrder.length)) {
data.defer = true;
setTimeout(() => {
initDataState('read', data, null);
gc();
persistData();
clearDataState();
data.defer = false;
});
}
}
};

Expand Down Expand Up @@ -230,7 +233,6 @@ export const make = (queryRootKey: string): InMemoryData => ({
persist: new Set(),
queryRootKey,
refCount: new Map(),
refLock: new Map(),
links: {
optimistic: new Map(),
base: new Map(),
Expand All @@ -241,6 +243,7 @@ export const make = (queryRootKey: string): InMemoryData => ({
},
deferredKeys: new Set(),
commutativeKeys: new Set(),
dirtyKeys: new Set(),
optimisticOrder: [],
storage: null,
});
Expand Down Expand Up @@ -314,41 +317,23 @@ const getNode = <T>(
};

/** Adjusts the reference count of an entity on a refCount dict by "by" and updates the gc */
const updateRCForEntity = (
gc: undefined | Set<string>,
refCount: KeyMap<number>,
entityKey: string,
by: number
): void => {
const updateRCForEntity = (entityKey: string, by: number): void => {
// Retrieve the reference count and adjust it by "by"
const count = refCount.get(entityKey) || 0;
const newCount = count + by;
refCount.set(entityKey, newCount);
const count = currentData!.refCount.get(entityKey) || 0;
const newCount = count + by > 0 ? count + by : 0;
currentData!.refCount.set(entityKey, newCount);
// Add it to the garbage collection batch if it needs to be deleted or remove it
// from the batch if it needs to be kept
if (gc) {
if (newCount <= 0) gc.add(entityKey);
else if (count <= 0 && newCount > 0) gc.delete(entityKey);
}
if (!newCount) currentData!.gc.add(entityKey);
else if (!count && newCount) currentData!.gc.delete(entityKey);
};

/** Adjusts the reference counts of all entities of a link on a refCount dict by "by" and updates the gc */
const updateRCForLink = (
gc: undefined | Set<string>,
refCount: KeyMap<number>,
link: Link | undefined,
by: number
): void => {
if (typeof link === 'string') {
updateRCForEntity(gc, refCount, link, by);
} else if (Array.isArray(link)) {
for (let i = 0, l = link.length; i < l; i++) {
if (Array.isArray(link[i])) {
updateRCForLink(gc, refCount, link[i], by);
} else if (link[i]) {
updateRCForEntity(gc, refCount, link[i] as string, by);
}
}
const updateRCForLink = (link: Link | undefined, by: number): void => {
if (Array.isArray(link)) {
for (let i = 0, l = link.length; i < l; i++) updateRCForLink(link[i], by);
} else if (typeof link === 'string') {
updateRCForEntity(link, by);
}
};

Expand Down Expand Up @@ -391,40 +376,28 @@ const extractNodeMapFields = <T>(

/** Garbage collects all entities that have been marked as having no references */
export const gc = () => {
// If we're currently awaiting deferred results, abort GC run
if (currentData!.optimisticOrder.length) return;

// Iterate over all entities that have been marked for deletion
// Entities have been marked for deletion in `updateRCForEntity` if
// their reference count dropped to 0
const { gc: batch } = currentData!;
for (const entityKey of batch.keys()) {
// Check first whether the reference count is still 0
const rc = currentData!.refCount.get(entityKey) || 0;
if (rc > 0) {
batch.delete(entityKey);
return;
}
for (const entityKey of currentData!.gc.keys()) {
// Remove the current key from the GC batch
currentData!.gc.delete(entityKey);

// Each optimistic layer may also still contain some references to marked entities
for (const layerKey of currentData!.refLock.keys()) {
const refCount = currentData!.refLock.get(layerKey);
if (refCount) {
const locks = refCount.get(entityKey) || 0;
// If the optimistic layer has any references to the entity, don't GC it,
// otherwise delete the reference count from the optimistic layer
if (locks > 0) return;
refCount.delete(entityKey);
}
}
// Check first whether the entity has any references,
// if so, we skip it from the GC run
const rc = currentData!.refCount.get(entityKey) || 0;
if (rc > 0) continue;

// Delete the reference count, and delete the entity from the GC batch
currentData!.refCount.delete(entityKey);
batch.delete(entityKey);
currentData!.records.base.delete(entityKey);
const linkNode = currentData!.links.base.get(entityKey);
if (linkNode) {
currentData!.links.base.delete(entityKey);
for (const fieldKey in linkNode) {
updateRCForLink(batch, currentData!.refCount, linkNode[fieldKey], -1);
}
for (const fieldKey in linkNode) updateRCForLink(linkNode[fieldKey], -1);
}
}
};
Expand Down Expand Up @@ -484,39 +457,20 @@ export const writeLink = (
fieldKey: string,
link?: Link | undefined
) => {
const data = currentData!;
// Retrieve the reference counting dict or the optimistic reference locking dict
let refCount: KeyMap<number> | undefined;
// Retrive the link NodeMap from either an optimistic or the base layer
let links: KeyMap<Dict<Link | undefined>> | undefined;
// Set the GC batch if we're not optimistically updating
let gc: undefined | Set<string>;
if (currentOptimisticKey) {
// The refLock counters are also reference counters, but they prevent
// garbage collection instead of being used to trigger it
refCount = data.refLock.get(currentOptimisticKey);
if (!refCount)
data.refLock.set(currentOptimisticKey, (refCount = new Map()));
links = data.links.optimistic.get(currentOptimisticKey);
} else {
refCount = data.refCount;
links = data.links.base;
gc = data.gc;
// Retrieve the link NodeMap from either an optimistic or the base layer
const links = currentOptimisticKey
? currentData!.links.optimistic.get(currentOptimisticKey)
: currentData!.links.base;
// Update the reference count for the link
if (!currentOptimisticKey) {
updateRCForLink(links?.get(entityKey)?.[fieldKey], -1);
updateRCForLink(link, 1);
}

// Retrieve the previous link for this field
const prevLinkNode = links && links.get(entityKey);
const prevLink = prevLinkNode && prevLinkNode[fieldKey];

// Update persistence batch and dependencies
updateDependencies(entityKey, fieldKey);
updatePersist(entityKey, fieldKey);
// Update the link
setNode(data.links, entityKey, fieldKey, link);
// First decrease the reference count for the previous link
updateRCForLink(gc, refCount, prevLink, -1);
// Then increase the reference count for the new link
updateRCForLink(gc, refCount, link, 1);
setNode(currentData!.links, entityKey, fieldKey, link);
};

/** Reserves an optimistic layer and preorders it */
Expand All @@ -538,7 +492,7 @@ export const reserveLayer = (
index = index > -1 ? index : 0;
index < data.optimisticOrder.length &&
!data.deferredKeys.has(data.optimisticOrder[index]) &&
(!data.refLock.has(data.optimisticOrder[index]) ||
(!data.dirtyKeys.has(data.optimisticOrder[index]) ||
!data.commutativeKeys.has(data.optimisticOrder[index]));
index++
);
Expand All @@ -563,17 +517,17 @@ const createLayer = (data: InMemoryData, layerKey: number) => {
data.optimisticOrder.unshift(layerKey);
}

if (!data.refLock.has(layerKey)) {
data.refLock.set(layerKey, new Map());
if (!data.dirtyKeys.has(layerKey)) {
data.dirtyKeys.add(layerKey);
data.links.optimistic.set(layerKey, new Map());
data.records.optimistic.set(layerKey, new Map());
}
};

/** Clears all links and records of an optimistic layer */
const clearLayer = (data: InMemoryData, layerKey: number) => {
if (data.refLock.has(layerKey)) {
data.refLock.delete(layerKey);
if (data.dirtyKeys.has(layerKey)) {
data.dirtyKeys.delete(layerKey);
data.records.optimistic.delete(layerKey);
data.links.optimistic.delete(layerKey);
data.deferredKeys.delete(layerKey);
Expand Down

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