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fix: track blob refcounts so prune does not delete shared files #68

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fix: track blob refcounts so prune does not delete shared files #68

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1 change: 1 addition & 0 deletions common/build.gradle.kts
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,7 @@ dependencies {
api("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.9.0")
api("org.jetbrains.kotlinx:kotlinx-serialization-json:1.7.0")
api("org.jetbrains.kotlinx:atomicfu:0.26.0")
testImplementation("org.jetbrains.kotlin:kotlin-test-junit:2.0.21")
}

tasks {
Expand Down
108 changes: 99 additions & 9 deletions common/src/main/kotlin/com/github/zly2006/xbackup/BackupDatabaseService.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@ import org.jetbrains.exposed.sql.transactions.TransactionManager
import org.jetbrains.exposed.sql.transactions.experimental.newSuspendedTransaction
import org.jetbrains.exposed.sql.transactions.transaction
import org.slf4j.LoggerFactory
import java.io.ByteArrayInputStream
import java.io.ByteArrayOutputStream
import java.io.File
import java.io.IOException
Expand Down Expand Up @@ -61,6 +62,7 @@ class BackupDatabaseService(
BackupEntryBackupTable,
withLogs = false
)
ensureBlobRefTable()
}
}

Expand Down Expand Up @@ -118,6 +120,12 @@ class BackupDatabaseService(
val entry = reference("entry", BackupEntryTable, ReferenceOption.CASCADE).index()
}

object BlobRefTable : Table("blob_refs") {
val hash = varchar("hash", 255)
val refCount = integer("ref_count")
override val primaryKey = PrimaryKey(hash)
}

@Serializable
data class BackupEntry(
override val id: Int,
Expand Down Expand Up @@ -145,6 +153,10 @@ class BackupDatabaseService(
suspend fun getInputStreamInternal(service: BackupDatabaseService): InputStream? {
val blob = service.getBlobFile(hash)
if (!blob.exists()) {
if (hash == EMPTY_BLOB_HASH) {
service.ensureEmptyBlobExists()
return ByteArrayInputStream(ByteArray(0))
}
return null
}
try {
Expand Down Expand Up @@ -378,6 +390,7 @@ class BackupDatabaseService(
it[this.backup] = backup.id
it[this.entry] = entry.id
}
incrementBlobRef(entry.hash)
}
// recheck
val entryList = backup.entries.filter {
Expand Down Expand Up @@ -408,12 +421,12 @@ class BackupDatabaseService(
suspend fun deleteBackupInternal(backup: IBackup) {
syncDbQuery {
backup.entries.forEach { entry ->
decrementBlobRef(entry.hash)
if (BackupEntryBackupTable.selectAll().where {
BackupEntryBackupTable.entry eq entry.id and
(BackupEntryBackupTable.backup neq backup.id)
}.empty()
) {
getBlobFile(entry.hash).toFile().delete()
BackupEntryTable.deleteWhere {
id eq entry.id
}
Expand Down Expand Up @@ -567,9 +580,12 @@ class BackupDatabaseService(
override fun check(backup: IBackup): Boolean {
var valid = true
backup.entries.forEach {
val blobFile = getBlobFile(it.hash)
if (it.isDirectory) return@forEach
else if (!blobFile.exists()) {
if (it.hash == EMPTY_BLOB_HASH) {
ensureEmptyBlobExists()
}
val blobFile = getBlobFile(it.hash)
if (!blobFile.exists()) {
log.error("Blob not found for file ${it.path}, hash: ${it.hash}")
valid = false
}
Expand Down Expand Up @@ -701,13 +717,11 @@ class BackupDatabaseService(

suspend fun deleteUnusedBlobs(): Int {
val used = dbQuery {
val column = Substring(BackupEntryTable.hash, intLiteral(3), intLiteral(30))
BackupEntryTable.select(
column // 32 -2 = 30
).withDistinct(true).map { row -> row[column] }
}.toSet()
BlobRefTable.selectAll().map { row -> row[BlobRefTable.hash].drop(2) }.toSet()
}
val emptyBlobName = EMPTY_BLOB_HASH.drop(2)
val unused = getBlobFile("").toFile().walk().filter { it.isFile }.filterNot {
it.name in used
it.name == emptyBlobName || it.name in used
}.toList()
log.info("Deleting ${unused.size} unused blobs")
unused.forEach {
Expand Down Expand Up @@ -746,7 +760,83 @@ class BackupDatabaseService(
TransactionManager.closeAndUnregister(database)
}

private fun Transaction.blobRefsTableExists(): Boolean {
return exec("SELECT 1 FROM sqlite_master WHERE type='table' AND name='blob_refs'") { rs ->
rs.next()
} == true
}

private fun Transaction.ensureBlobRefTable() {
if (blobRefsTableExists()) {
return
}
SchemaUtils.create(BlobRefTable)
val countCol = BackupEntryBackupTable.id.count()
(BackupEntryBackupTable innerJoin BackupEntryTable)
.select(BackupEntryTable.hash, countCol)
.where {
(BackupEntryTable.hash neq "") and (BackupEntryTable.hash neq EMPTY_BLOB_HASH)
}
.groupBy(BackupEntryTable.hash)
.forEach { row ->
BlobRefTable.insert {
it[hash] = row[BackupEntryTable.hash]
it[refCount] = row[countCol].toInt()
}
}
log.info("Initialized blob_refs from existing backups")
}

private fun Transaction.tracksBlobRef(hash: String): Boolean {
return hash.isNotEmpty() && hash != EMPTY_BLOB_HASH
}

private fun Transaction.incrementBlobRef(hash: String) {
if (!tracksBlobRef(hash)) return
val existing = BlobRefTable.selectAll().where { BlobRefTable.hash eq hash }.firstOrNull()
if (existing == null) {
BlobRefTable.insert {
it[this.hash] = hash
it[refCount] = 1
}
} else {
val next = existing[BlobRefTable.refCount] + 1
BlobRefTable.update({ BlobRefTable.hash eq hash }) {
it[refCount] = next
}
}
}

private fun Transaction.decrementBlobRef(hash: String) {
if (!tracksBlobRef(hash)) return
val existing = BlobRefTable.selectAll().where { BlobRefTable.hash eq hash }.firstOrNull() ?: return
val next = existing[BlobRefTable.refCount] - 1
if (next <= 0) {
getBlobFile(hash).toFile().delete()
BlobRefTable.deleteWhere { BlobRefTable.hash eq hash }
} else {
BlobRefTable.update({ BlobRefTable.hash eq hash }) {
it[refCount] = next
}
}
}

internal fun ensureEmptyBlobExists() {
val blob = getBlobFile(EMPTY_BLOB_HASH)
if (!blob.exists()) {
blob.createParentDirectories()
blob.writeBytes(ByteArray(0))
}
}

internal fun blobRefCount(hash: String): Int? = transaction {
BlobRefTable.selectAll().where { BlobRefTable.hash eq hash }
.firstOrNull()?.get(BlobRefTable.refCount)
}

companion object {
const val EMPTY_BLOB_HASH = "d41d8cd98f00b204e9800998ecf8427e"

private fun ResultRow.toBackup(): Backup {
val id = this[BackupTable.id].value
val entries = BackupEntryBackupTable.select(BackupEntryBackupTable.entry).where {
Expand Down
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