When using the SQLitecache, must I ensure the machine is a primary?

[warronbebster]

I've followed the caching docs and when I run it in production, I get Disk I/O SQLite errors:

2025-09-04T19:33:55Z app[784049ef491948] iad [info]level=INFO msg="fuse: write(): wal error: read only replica"
error setting cache: challenge:mallorca-championships-presented-by-ecotrans-group-2025-served-2025 Error: disk I/O error
2025-09-04T19:33:55Z app[784049ef491948] iad [info]    at Object.set (file:///myapp/app/utils/cache.server.ts:154:16)
2025-09-04T19:33:55Z app[784049ef491948] iad [info]    at getFreshValue (file:///myapp/node_modules/@epic-web/cachified/src/getFreshValue.ts:65:19)
2025-09-04T19:33:55Z app[784049ef491948] iad [info]    at cachified (file:///myapp/node_modules/@epic-web/cachified/src/cachified.ts:94:17)
2025-09-04T19:33:55Z app[784049ef491948] iad [info]    at getChallenge (file:///myapp/app/utils/challenge.server.ts:32:18)
2025-09-04T19:33:55Z app[784049ef491948] iad [info]    at getTournamentContextMain (file:///myapp/app/utils/tournament-context.server.ts:60:18)
2025-09-04T19:33:55Z app[784049ef491948] iad [info]    at loader$9 (file:///myapp/app/routes/tournaments+/$slug+/$tour+/index.tsx:38:9)
2025-09-04T19:33:55Z app[784049ef491948] iad [info]    at callRouteHandler (file:///myapp/node_modules/react-router/dist/development/chunk-5UALIXAM.mjs:509:16)
2025-09-04T19:33:55Z app[784049ef491948] iad [info]    at commonRoute.loader (file:///myapp/node_modules/react-router/dist/development/chunk-5UALIXAM.mjs:658:19)
2025-09-04T19:33:55Z app[784049ef491948] iad [info]    at file:///myapp/node_modules/react-router/dist/development/chunk-PVWAREVJ.mjs:4259:19
2025-09-04T19:33:55Z app[784049ef491948] iad [info]    at callLoaderOrAction (file:///myapp/node_modules/react-router/dist/development/chunk-PVWAREVJ.mjs:4311:16) {
2025-09-04T19:33:55Z app[784049ef491948] iad [info]  code: 'ERR_SQLITE_ERROR',
2025-09-04T19:33:55Z app[784049ef491948] iad [info]  errcode: 778,
2025-09-04T19:33:55Z app[784049ef491948] iad [info]  errstr: 'disk I/O error'
2025-09-04T19:33:55Z app[784049ef491948] iad [info]}

To use the SQLite cache, do we have to first use ensurePrimary() before saving to it? If so, can the docs be updated to reflect that?

[kentcdodds]

How are you using it? Are you trying to write to it directly? It's intended to be used with cachified (in the cache.server.ts file). That handles updating the cache for you in an efficient way.

[warronbebster]

I basically copied the implementation from the docs, using cachified:

const topPredictions = await cachified({
	key: `tournament:topPredictions:v1:${tournament.slug}:${challenge ? challenge.id : 'no-challenge'}`,
	cache: cache,
	ttl: 1_800_000, // 30 minutes
	staleWhileRevalidate: 1_200_000, // 20 minutes
	async getFreshValue() {
		return prisma.userPrediction.findMany({
			where: {
				tournamentId: tournament.id,
				challengeId: challenge ? challenge.id : null,
			},
			orderBy: { score: 'desc' },
			take: 10,
			include: { user: { select: { username: true } } },
		})
	},
})

[kentcdodds]

Whoops! I made a mistake by removing the utility that made the cache multi-region safe. I've just pushed this commit to fix it: a1b3aa4

My apologies! Thank you for bringing it up.

As a note, you wouldn't want to use ensurePrimary for this because so many requests result in a cache update that you'd pretty much never benefit from having multiple regions. So instead we trigger a request to the primary when the cache needs to be updated.

[warronbebster]

Ah, thanks!! I thought I was going crazy.