Overleaf/services/history-v1/storage/lib/persist_buffer.js

// @ts-check
'use strict'

const logger = require('@overleaf/logger')
const OError = require('@overleaf/o-error')
const assert = require('./assert')
const chunkStore = require('./chunk_store')
const { BlobStore } = require('./blob_store')
const BatchBlobStore = require('./batch_blob_store')
const persistChanges = require('./persist_changes')
const redisBackend = require('./chunk_store/redis')

/**
 * Persist the changes from Redis buffer to the main storage
 *
 * Algorithm Outline:
 * 1. Get the latest chunk's endVersion from the database
 * 2. Get non-persisted changes from Redis that are after this endVersion.
 * 3. If no such changes, exit.
 * 4. Load file blobs for these Redis changes.
 * 5. Run the persistChanges() algorithm to store these changes into a new chunk(s) in GCS.
 *    - This must not decrease the endVersion. If changes were processed, it must advance.
 * 6. Set the new persisted version (endVersion of the latest persisted chunk) in Redis.
 *
 * @param {string} projectId
 * @param {Object} limits
 * @throws {Error | OError} If a critical error occurs during persistence.
 */
async function persistBuffer(projectId, limits) {
  assert.projectId(projectId)
  logger.debug({ projectId }, 'starting persistBuffer operation')

  // 1. Get the latest chunk's endVersion from GCS/main store
  let endVersion
  const latestChunkMetadata = await chunkStore.getLatestChunkMetadata(projectId)

  if (latestChunkMetadata) {
    endVersion = latestChunkMetadata.endVersion
  } else {
    endVersion = 0 // No chunks found, start from version 0
    logger.debug({ projectId }, 'no existing chunks found in main storage')
  }

  logger.debug({ projectId, endVersion }, 'got latest persisted chunk')

  // 2. Get non-persisted changes from Redis
  const changesToPersist = await redisBackend.getNonPersistedChanges(
    projectId,
    endVersion
  )

  if (changesToPersist.length === 0) {
    logger.debug(
      { projectId, endVersion },
      'no new changes in Redis buffer to persist'
    )
    // No changes to persist, update the persisted version in Redis
    // to match the current endVersion.  This shouldn't be needed
    // unless a worker failed to update the persisted version.
    await redisBackend.setPersistedVersion(projectId, endVersion)
    return
  }

  logger.debug(
    {
      projectId,
      endVersion,
      count: changesToPersist.length,
    },
    'found changes in Redis to persist'
  )

  // 4. Load file blobs for these Redis changes. Errors will propagate.
  const blobStore = new BlobStore(projectId)
  const batchBlobStore = new BatchBlobStore(blobStore)

  const blobHashes = new Set()
  for (const change of changesToPersist) {
    change.findBlobHashes(blobHashes)
  }
  if (blobHashes.size > 0) {
    await batchBlobStore.preload(Array.from(blobHashes))
  }
  for (const change of changesToPersist) {
    await change.loadFiles('lazy', blobStore)
  }

  // 5. Run the persistChanges() algorithm. Errors will propagate.
  logger.debug(
    {
      projectId,
      endVersion,
      changeCount: changesToPersist.length,
    },
    'calling persistChanges'
  )

  const persistResult = await persistChanges(
    projectId,
    changesToPersist,
    limits,
    endVersion
  )

  if (!persistResult || !persistResult.currentChunk) {
    throw new OError(
      'persistChanges did not produce a new chunk for non-empty changes',
      {
        projectId,
        endVersion,
        changeCount: changesToPersist.length,
      }
    )
  }

  const newPersistedChunk = persistResult.currentChunk
  const newEndVersion = newPersistedChunk.getEndVersion()

  if (newEndVersion <= endVersion) {
    throw new OError(
      'persisted chunk endVersion must be greater than current persisted chunk end version for non-empty changes',
      {
        projectId,
        newEndVersion,
        endVersion,
        changeCount: changesToPersist.length,
      }
    )
  }

  logger.debug(
    {
      projectId,
      oldVersion: endVersion,
      newVersion: newEndVersion,
    },
    'successfully persisted changes from Redis to main storage'
  )

  // 6. Set the persisted version in Redis. Errors will propagate.
  const status = await redisBackend.setPersistedVersion(
    projectId,
    newEndVersion
  )

  if (status !== 'ok') {
    throw new OError('failed to update persisted version in Redis', {
      projectId,
      newEndVersion,
      status,
    })
  }

  logger.debug(
    { projectId, newEndVersion },
    'updated persisted version in Redis'
  )

  logger.debug(
    { projectId, finalPersistedVersion: newEndVersion },
    'persistBuffer operation completed successfully'
  )
}

module.exports = persistBuffer