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Fix/default to maindb if read replica errs #1221

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merged 4 commits into from
Jun 5, 2024
Merged

Fix/default to maindb if read replica errs #1221

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fc40295
fix: catch errors and log if calls to read replica fail
May 31, 2024
74aa9ff
chore: format
May 31, 2024
0fd79ff
chore: fix for read replica
May 31, 2024
c10f1c5
feat: make replica connection optional
Jun 4, 2024
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16 changes: 13 additions & 3 deletions src/services/request-service.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -56,7 +56,12 @@ export class RequestService {
* @returns The request.
*/
async getStatusForCid(cid: CID): Promise<OutputOf<typeof CASResponse> | { error: string }> {
let request = await this.replicationRequestRepository.findByCid(cid)
let request
try {
request = await this.replicationRequestRepository.findByCid(cid)
} catch (e) {
logger.err(`Error fetching request from replica db for ${cid}, error: ${e}`)
}
if (!request) {
logger.debug(`Request not found in replica db for ${cid}, fetching from main_db`)
Metrics.count(METRIC_NAMES.REPLICA_DB_REQUEST_NOT_FOUND, 1)
Expand All @@ -79,11 +84,16 @@ export class RequestService {
* @returns The request.
*/
async findByCid(cid: CID): Promise<OutputOf<typeof CASResponse> | undefined> {
let found = await this.replicationRequestRepository.findByCid(cid)
let found
try {
found = await this.replicationRequestRepository.findByCid(cid)
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My preference would be to expect the replica to work if it exists, but default the config to main if there is none defined. I think we should expect it to work if it's defined, but it should be optional.

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In terms of implementation, I'd expect we either set up a RO connection pool, or we just use the main pool and the app still calls replicationRequestRepository for all reads because it doesn't require the writer, without needing to know anything about the actual DB used.

This also avoids doing double reads for things that don't actually exist and potentially getting hung trying to talk to a non-exists RO instance.

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yeah, it all around a better design to make the read replication optional. FYI, currently all our reads do not got to the replica. If the configuration for the read replica is not specified or if any of the config params are missing, we default to the maindb. Will add a commit for this and tag you, let me know if this might fix it or there might be something else I missed

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I like the changes you made, do we still need this fallback? if it fails now, it seems like it's failing for a reason so there's not sure we need to try another database.

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@samika98 samika98 Jun 5, 2024 •
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yup, in the case of the read replica not having the request. If sync b/w the db's is slow

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Yeah, what I was trying to say is that if the RR doesn't have the request, it's unlikely the main DB does so there's no reason to ask. If for some reason we're far enough behind on replicating (i.e. minutes), we probably don't want to load the main database more and should investigate. Otherwise, we can tolerate the client retrying again in a few seconds and the RR will respond with data.

} catch (e) {
logger.err(`Error fetching request from replica db for ${cid}, error: ${e}`)
}
if (!found) {
found = await this.requestRepository.findByCid(cid)
logger.debug(`Request not found in replica db for ${cid}, fetching from main_db`)
Metrics.count(METRIC_NAMES.REPLICA_DB_REQUEST_NOT_FOUND, 1)
found = await this.requestRepository.findByCid(cid)
if (!found) {
throw new RequestDoesNotExistError(cid)
}
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