Files
usenet-indexer/app/services/prefetcher.ts
T
Daan MeijerandClaude Opus 5.5 cfce8884d4
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Lone articles under scrambled names are per-article; inactive groups get no corpus fill
One article of a multi-part file under a name like "nYDeXeF49dieZ1J7flK-JFzZ3j.ZEDsr" or
"bslXlwgPiqZadhRa" (a random subject and poster per article, with fake counters) was a release:
looksRandom misses these names for their separators. 160k of alt.binaries.storage's 162k
non-Bob releases, and about 60% of all single-article releases in a 2% sample.

looks_scrambled / isScrambledFile: at least half the stem's letters and digits in tokens of 5+
that switch case or letter/digit 3 times or more (93% of the storage spam). Used for lone
articles given up before the block's end only; at the end the strict looksRandom stays, as the
rest of such a file can be in the next block. The namer's re-index (partialFiles) does the same.

The prefetcher's corpus fill skips groups that aren't active.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-29 22:19:11 +01:00

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import db from '@adonisjs/lucid/services/db'
import logger from '@adonisjs/core/services/logger'
import coordinatorConfig from '#config/coordinator'
import NntpPool from '#services/nntp_pool'
import Spool, { type ChunkSpan } from '#services/spool'
import Corpus, { type CorpusFilter } from '#services/corpus'
import RuleSets from '#services/rule_sets'
import CatalogSpace from '#services/catalog_space'
import { hedge, type Request, type XoverClient } from '#lib/nntp/index'
interface Target {
id: number
group: string
/** Chunk starts to fetch without compression (ranges.plain_chunks). */
plain: Set<number>
/** Chunks not spooled yet, in order. */
missing: ChunkSpan[]
/** All of the range's chunks, from its start. */
total: number
start: number
end: number
/** Its chunks are kept in the corpus (ranges.capture), and read from there when stored. */
capture: boolean
/** Fetched into the corpus only, not the spool: a capture range no worker leases soon (corpus.ahead). */
corpusOnly?: boolean
}
/** A request's bytes in are sampled this often; STALL_SAMPLES of them make the minute a stall is judged over. */
const STALL_SAMPLE_MS = 15_000
const STALL_SAMPLES = 60_000 / STALL_SAMPLE_MS
/** Connection ages the report counts slow first requests by, in minutes. */
const AGE_BUCKETS = [2, 10, Infinity]
/** How often the targets are read again from the database. */
const REFRESH_MS = 2000
/** How often the spool's size is measured (a stat per file). */
const SIZE_MS = 30_000
/**
* Keeps the news server busy ahead of the workers (REBUILD.md, prefetch).
* Every connection takes the next missing chunk: the leased ranges' first
* (a worker waits for them), then the next planned ranges, with at most
* PREFETCH_PER_RANGE connections on a range and PREFETCH_PER_GROUP on a
* group (Eweka answers faster spread out), about SPOOL_AHEAD_PER_LEASE per
* active lease (at least SPOOL_MIN_AHEAD), within SPOOL_MAX_GB. One
* connection fills ~26 k overview lines/s, so a range on one connection
* kept its worker waiting (LOG.md 2026-10-09). A chunk that takes long is
* asked again on a spare connection (fetchHedged).
*/
export class Prefetcher {
/**
* This process's share of the ranges, `id % count = index` (`coordinator:run --shard`): one
* process's event loop handles ~60 MB/s of compressed XOVER (16.5% of a core at ~10 MB/s;
* LOG.md 2026-10-09), less than 50 connections bring.
*/
constructor(private shard = { index: 0, count: 1 }) {}
private targets: Target[] = []
private claimed = new Set<string>()
/** Chunks being fetched per range and per group (spool.perRange, spool.perGroup). */
private perRange = new Map<number, number>()
private perGroup = new Map<string, number>()
private running = 0
private refreshedAt = 0
private stopped = false
private spoolBytes = 0
private sizedAt = 0
/** Fetched since the last report: chunks, articles, ms spent fetching. */
private stats = this.freshStats()
/** Loops in a fetch or a spool write right now. */
private fetchingNow = 0
private writingNow = 0
private sampler?: NodeJS.Timeout
/** Requests in flight: what, since when, on which connection (the report names the oldest). */
private inFlight = new Set<{
rangeId: number
from: number
to: number
since: number
client: XoverClient
}>()
/** Capture ranges found complete in the corpus (not looked at again). */
private stored = new Set<number>()
private freshStats() {
return {
chunks: 0,
/** Chunks read from the corpus instead of fetched. */
stored: 0,
/** Chunks fetched into the corpus only (corpus.ahead). */
captured: 0,
articles: 0,
fetchMs: 0,
hedged: 0,
hedgeWon: 0,
/** First requests per connection-age bucket, and how many of them were slow. */
byAge: AGE_BUCKETS.map(() => ({ requests: 0, slow: 0 })),
/** Spool writes and the range's update, ms. */
writeMs: 0,
/** Per answered request, ms: GROUP, XOVER until its status line, the transfer; transfers with a silence over 5 s. */
requests: 0,
groupMs: 0,
replyMs: 0,
bodyMs: 0,
silent: 0,
/** Once a second: loops fetching, writing, not running; pool connections with a command in flight. */
samples: 0,
fetching: 0,
writing: 0,
idle: 0,
inFlight: 0,
inFlightMin: Infinity,
/** Requests given up as stalled (nntpStallBytesPerMinute). */
deadlines: 0,
ranges: 0,
groups: 0,
since: Date.now(),
}
}
/** The prefetcher's loops: the pool less the connections kept for hedging. */
private get loops() {
return Math.max(1, NntpPool.size - coordinatorConfig.nntpHedgeConnections)
}
/** One round: refreshes the targets now and then, and puts idle connections to work. */
async tick() {
this.sampler ??= setInterval(() => this.sample(), 1000).unref()
if (Date.now() - this.refreshedAt >= REFRESH_MS) {
this.refreshedAt = Date.now()
this.targets = await this.readTargets()
}
this.report()
while (!this.stopped && this.running < this.loops && this.peek()) {
this.running++
this.work()
.catch((error) => logger.warn(`Prefetching: ${error.message}`))
.finally(() => this.running--)
}
// Work left with every loop running: the pool's share could be bigger.
if (!this.stopped && this.running >= this.loops && this.peek()) NntpPool.starved()
}
stop() {
this.stopped = true
clearInterval(this.sampler)
}
get active() {
return this.running
}
/** One connection's loop: chunks until there is nothing left to fetch. */
private async work() {
while (!this.stopped) {
// The pool's share got smaller: fewer loops (waiting on the pool, they'd count as work short of a connection).
// Two leaving at once is one too many for a tick (TICK_MS), whose loop comes back.
if (this.running > this.loops) return
const next = this.take()
if (!next) return
const { target, span } = next
try {
const fetchedAt = Date.now()
this.fetchingNow++
const fetch = async (client: Parameters<Parameters<typeof NntpPool.use>[0]>[0]) => {
await client.group(target.group)
return client.xoverRaw(span.from, span.to)
}
const corpusRange = { group: target.group, start: target.start, end: target.end }
// A range in the corpus is read from disk (a reset re-indexes it without the news server).
let data =
target.capture && !target.corpusOnly ? await Corpus.read(corpusRange, span) : null
const stored = data !== null
try {
if (!data)
data = target.plain.has(span.from)
? await NntpPool.usePlain(fetch)
: await this.fetchHedged(target.id, target.group, span)
} finally {
this.fetchingNow--
}
if (stored) {
this.stats.stored++
} else {
this.stats.chunks++
this.stats.articles += span.to - span.from + 1
this.stats.fetchMs += Date.now() - fetchedAt
if (target.capture)
await Corpus.write(corpusRange, span, data, target.total, await this.corpusFilter())
}
if (target.corpusOnly) {
this.stats.captured++
continue
}
const writtenAt = Date.now()
this.writingNow++
try {
const existed = await Spool.has(target.id, span)
await Spool.write(target.id, span, data)
if (existed) continue
this.spoolBytes += data.length
const { rows } = await db.rawQuery(
`UPDATE ranges SET spooled_chunks = spooled_chunks + 1 WHERE id = ? RETURNING spooled_chunks`,
[target.id]
)
if (Number(rows[0]?.spooled_chunks) >= target.total)
await db.from('ranges').where('id', target.id).update({ spooled_at: new Date() })
} finally {
this.writingNow--
this.stats.writeMs += Date.now() - writtenAt
}
} finally {
this.claimed.delete(`${target.id}:${span.from}`)
this.count(target, -1)
}
}
}
/**
* A chunk over a pooled connection. Not in after nntpHedgeAfterMs, it's
* asked again on a free connection (if there is one): Eweka stalls single
* requests, and the same chunk on another connection mostly comes in
* seconds (LOG.md 2026-10-09 (15)). The first answer wins; the other
* request can't be cancelled, so its connection is closed (the pool opens
* a fresh one).
*/
private async fetchHedged(rangeId: number, group: string, span: ChunkSpan): Promise<Buffer> {
let age: number | undefined
const request = (
start: (work: (client: XoverClient) => Promise<Buffer>) => Promise<Buffer> | null,
first: boolean
): Request<Buffer> | null => {
let client: XoverClient | undefined
let cancelled = false
const done = start(async (c) => {
// Given up before it got a connection: the connection goes back unused.
if (cancelled) return Buffer.alloc(0)
client = c
if (first) age = NntpPool.ageOf(c)
const entry = { rangeId, from: span.from, to: span.to, since: Date.now(), client: c }
this.inFlight.add(entry)
// Bytes in, sampled every STALL_SAMPLE_MS: less than nntpStallBytesPerMinute over the last minute is a stall.
let late = false
const samples: number[] = []
const watch = setInterval(() => {
samples.push(c.buffered)
if (samples.length <= STALL_SAMPLES) return
const minuteAgo = samples.shift()!
if (c.buffered - minuteAgo < coordinatorConfig.nntpStallBytesPerMinute) {
late = true
this.stats.deadlines++
c.close()
}
}, STALL_SAMPLE_MS)
let data: Buffer
let groupMs = 0
try {
const groupAt = performance.now()
await c.group(group)
groupMs = performance.now() - groupAt
data = await c.xoverRaw(span.from, span.to)
} catch (error) {
if (!late) throw error
throw new Error(
`Chunk ${span.from}–${span.to} of range ${rangeId} stalled (under ${coordinatorConfig.nntpStallBytesPerMinute / 1000} kB in a minute, ${Math.round(c.buffered / 1000)} kB in); fetching it again`
)
} finally {
clearInterval(watch)
this.inFlight.delete(entry)
}
if (!cancelled) {
const t = c.lastTiming
this.stats.requests++
this.stats.groupMs += groupMs
this.stats.replyMs += t.replyMs
this.stats.bodyMs += t.bodyMs
if (t.longestGapMs > 5000) this.stats.silent++
}
return data
})
if (!done) return null
done.catch(() => {})
return {
done,
// The request can't be called off on the wire: its connection is closed, and the pool opens a fresh one.
cancel: () => {
cancelled = true
client?.close()
},
}
}
const result = await hedge(
() => request((work) => NntpPool.use(work), true)!,
() => request((work) => NntpPool.tryUse(work), false),
coordinatorConfig.nntpHedgeAfterMs
)
if (age !== undefined) {
const bucket = this.stats.byAge[AGE_BUCKETS.findIndex((minutes) => age! < minutes * 60_000)]
bucket.requests++
if (result.late) bucket.slow++
}
if (result.hedged) this.stats.hedged++
if (result.secondWon) this.stats.hedgeWon++
return result.value
}
/** The longest-running request: range, chunk, how long, how much came in. */
private oldest() {
let oldest:
{ rangeId: number; from: number; to: number; since: number; client: XoverClient } | undefined
for (const r of this.inFlight) if (!oldest || r.since < oldest.since) oldest = r
if (!oldest) return 'none in flight'
return `oldest request ${Math.round((Date.now() - oldest.since) / 1000)} s (range ${oldest.rangeId}, ${oldest.from}–${oldest.to}, ${Math.round(oldest.client.buffered / 1000)} kB in)`
}
private sample() {
const s = this.stats
s.samples++
s.fetching += this.fetchingNow
s.writing += this.writingNow
s.idle += Math.max(0, this.loops - this.fetchingNow - this.writingNow)
s.inFlight += NntpPool.busyCount
s.inFlightMin = Math.min(s.inFlightMin, NntpPool.busyCount)
s.ranges += this.perRange.size
s.groups += this.perGroup.size
}
/** A line a minute: what the connections fetched, and how long a chunk took. */
private report() {
const seconds = (Date.now() - this.stats.since) / 1000
if (seconds < 60) return
const { chunks, articles, fetchMs, hedged, hedgeWon, byAge, samples, requests } = this.stats
if (chunks > 0) {
const ages = byAge
.map((b, i) =>
`${i === 0 ? '<' : `${AGE_BUCKETS[i - 1]}–`}${AGE_BUCKETS[i] === Infinity ? '' : AGE_BUCKETS[i]} min ${b.slow}/${b.requests}`.replace(
'– min',
'+ min'
)
)
.join(', ')
logger.info(
`Prefetched ${chunks} chunks in ${seconds.toFixed(0)} s: ${Math.round(articles / seconds).toLocaleString('en')} articles/s, ` +
`${(fetchMs / chunks / 1000).toFixed(1)} s a chunk; ` +
`hedged ${hedged} (second won ${hedgeWon}); slow by connection age: ${ages}` +
(this.stats.stored > 0 ? `; ${this.stats.stored} chunks from the corpus` : '') +
(this.stats.captured > 0 ? `; ${this.stats.captured} fetched into the corpus only` : '') +
'.'
)
const st = this.stats
const avg = (n: number) => (samples > 0 ? n / samples : 0)
const per = (ms: number) => (requests > 0 ? (ms / requests / 1000).toFixed(1) : '-')
logger.info(
`Connections: ${avg(st.inFlight).toFixed(1)} of ${NntpPool.size} with a command in flight (min ${st.inFlightMin}), ` +
`on ${avg(st.ranges).toFixed(1)} ranges of ${avg(st.groups).toFixed(1)} groups; ` +
`loops ${avg(st.fetching).toFixed(1)} fetching, ${avg(st.writing).toFixed(1)} writing, ${avg(st.idle).toFixed(1)} idle; ` +
`a request: GROUP ${per(st.groupMs)} s, XOVER reply ${per(st.replyMs)} s, transfer ${per(st.bodyMs)} s; ` +
`${st.silent} of ${requests} transfers silent >5 s; writing ${(st.writeMs / Math.max(1, chunks)).toFixed(0)} ms a chunk; ` +
`${st.deadlines} stalled (under ${coordinatorConfig.nntpStallBytesPerMinute / 1000} kB a minute); ${this.oldest()}.`
)
}
this.stats = this.freshStats()
}
private peek(): boolean {
return this.targets.some(
(t) => this.open(t) && t.missing.some((s) => !this.claimed.has(`${t.id}:${s.from}`))
)
}
/** Whether the target is under its range's and its group's limit of connections. */
private open(target: Target) {
const { perRange, perGroup } = coordinatorConfig.spool
return (
(perRange <= 0 || (this.perRange.get(target.id) ?? 0) < perRange) &&
(perGroup <= 0 || (this.perGroup.get(target.group) ?? 0) < perGroup)
)
}
private count(target: Target, by: number) {
const range = (this.perRange.get(target.id) ?? 0) + by
const group = (this.perGroup.get(target.group) ?? 0) + by
if (range > 0) this.perRange.set(target.id, range)
else this.perRange.delete(target.id)
if (group > 0) this.perGroup.set(target.group, group)
else this.perGroup.delete(target.group)
}
/** The first unclaimed missing chunk, in target order, of a target under its limits. */
private take(): { target: Target; span: ChunkSpan } | null {
for (const target of this.targets) {
if (!this.open(target)) continue
const index = target.missing.findIndex((s) => !this.claimed.has(`${target.id}:${s.from}`))
if (index === -1) continue
const [span] = target.missing.splice(index, 1)
this.claimed.add(`${target.id}:${span.from}`)
this.count(target, 1)
return { target, span }
}
return null
}
private async readTargets(): Promise<Target[]> {
if (Date.now() - this.sizedAt >= SIZE_MS) {
this.sizedAt = Date.now()
this.spoolBytes = await Spool.size()
}
const mine = (q: any) =>
this.shard.count > 1 ? q.whereRaw('r.id % ? = ?', [this.shard.count, this.shard.index]) : q
const rows = (q: any) =>
mine(
q
.from('ranges as r')
.join('groups as g', 'g.id', 'r.group_id')
.select(
'r.id',
'g.name as group',
'r.start_id',
'r.end_id',
'r.next_id',
'r.plain_chunks',
'r.capture'
)
)
// Leased ranges, checked against the spool's files whatever spooled_at says: a worker waits for them.
const leased = await rows(db.query()).where('r.status', 'leased').orderBy('r.leased_at')
// The groups workers hold (group_leases; REBUILD.md design 1), by lane: the prefetcher runs ahead of their
// cursors (a group's history and tail lanes are two cursors).
const held: { group: number; lane: string }[] = (
await db
.from('group_leases')
.whereNotNull('node_id')
.where(
'heartbeat_at',
'>=',
new Date(Date.now() - coordinatorConfig.leaseTtlSeconds * 1000)
)
.select('group_id', 'lane')
).map((l) => ({ group: Number(l.group_id), lane: l.lane }))
// Planned ranges ahead: those started already, then new ones up to SPOOL_AHEAD_PER_LEASE per lease.
const ahead = Math.max(
coordinatorConfig.spool.minAhead,
coordinatorConfig.spool.aheadPerLease * Math.max(leased.length, held.length)
)
const started = await rows(db.query())
.where('r.status', 'planned')
.where('r.spooled_chunks', '>', 0)
.whereNull('r.spooled_at')
.orderBy([{ column: 'r.priority' }, { column: 'r.id' }])
const [{ ready }] = await mine(
db.from('ranges as r').where('r.status', 'planned').where('r.spooled_chunks', '>', 0)
).count('* as ready')
const room = this.spoolBytes < coordinatorConfig.spool.maxBytes
// With at most perRange connections a range, enough ranges still being fetched for all loops: fully
// spooled ones count as ready but need no connection (30 of 40 busy on small ranges; LOG.md 2026-10-10 (2)).
// 8 more than that: ranges with a chunk or two left take fewer than perRange (with +2, 3 of 40 loops idle).
const { perRange } = coordinatorConfig.spool
const short =
perRange > 0 ? Math.ceil(this.loops / perRange) + 8 - (leased.length + started.length) : 0
const want = Math.max(ahead - Number(ready), short)
// The catalog at its cap on the NVMe: no history fetched ahead (CatalogSpace).
const full = await CatalogSpace.full()
// Ahead of each held cursor: the lane's next ranges in article order (the history lane's within what the group
// leases hand out: LEASE_MIN/MAX_PRIORITY, LEASE_CAPTURE_ONLY, and none at the catalog's cap; the tail lane's
// at the tail's priority), a range of every held cursor before any cursor's second; without held groups (no
// window worker running) nothing is fetched ahead for workers.
const { leasePriorityMin, leasePriorityMax, leaseCaptureOnly } = coordinatorConfig
const tailPriority = coordinatorConfig.tail.priority
const heldHistory = full ? [] : held.filter((h) => h.lane === 'history').map((h) => h.group)
const heldTail = held.filter((h) => h.lane === 'tail').map((h) => h.group)
const fresh =
room && want > 0 && heldHistory.length + heldTail.length > 0
? await rows(db.query())
.where('r.status', 'planned')
.where('r.spooled_chunks', 0)
.whereRaw('r.next_id <= r.end_id')
.where((q: any) =>
q
.where((h: any) =>
h
.whereIn('r.group_id', heldHistory)
.where('r.priority', '>', tailPriority)
.whereBetween('r.priority', [leasePriorityMin, leasePriorityMax])
.where((c: any) => (leaseCaptureOnly ? c.where('r.capture', true) : c))
)
.orWhere((t: any) =>
t.whereIn('r.group_id', heldTail).where('r.priority', '<=', tailPriority)
)
)
.orderByRaw(
'row_number() OVER (PARTITION BY r.group_id, r.priority <= ? ORDER BY r.start_id), r.priority, r.start_id',
[tailPriority]
)
.limit(want)
: []
const targets: Target[] = []
for (const row of [...leased, ...(room ? started : []), ...fresh]) {
const start = Number(row.start_id)
const end = Number(row.end_id)
const total = Spool.chunksOf({ start, end }).length
const missing: ChunkSpan[] = []
// A chunk already in the corpus isn't spooled: the stream serves it from there (REBUILD.md design 1).
const corpusRange = row.capture === true ? { group: row.group as string, start, end } : null
for (const span of Spool.chunksOf({ start, end }, Number(row.next_id))) {
if (this.claimed.has(`${row.id}:${span.from}`) || (await Spool.has(Number(row.id), span)))
continue
if (corpusRange && (await Corpus.has(corpusRange, span))) continue
missing.push(span)
}
if (missing.length > 0) {
targets.push({
id: Number(row.id),
group: row.group,
plain: new Set((row.plain_chunks ?? []).map(Number)),
missing,
total,
start,
end,
capture: row.capture === true,
})
}
}
// Last, for loops with nothing else to do: capture ranges not stored yet, into the corpus only.
for (const target of await this.corpusTargets(rows, new Set(targets.map((t) => t.id))))
targets.push(target)
return targets
}
private filterRules: { at: number; filter: CorpusFilter } | null = null
/** The rules corpus chunks are filtered with (CORPUS_FILTER), read again once a minute; undefined when off. */
private async corpusFilter(): Promise<CorpusFilter | undefined> {
if (!coordinatorConfig.corpus.filter) return undefined
if (!this.filterRules || Date.now() - this.filterRules.at > 60_000) {
const rules = await RuleSets.current()
this.filterRules = {
at: Date.now(),
filter: { ruleVersion: rules.version, priorities: rules.priorities },
}
}
return this.filterRules.filter
}
/**
* Up to corpus.ahead capture ranges whose chunks aren't all in the corpus, by priority: planned ones not started
* (not leased soon), and done ones (a window of every group, ranges:capture, takes those indexed already too);
* as many of a group as its connections allow (perGroup / perRange): in id order the 16 were one group's, which
* took 4 of the loops and left the rest idle (30k articles/s; LOG.md 2026-10-23 (100)). The candidates are taken
* a range of every group at a time (the n-th unstored range of each group before any group's n+1-th): a group's
* ranges have consecutive ids, and once the small groups of a window were stored the 512 lowest ids were all one
* group's, two targets on two connections (10 ranges an hour; LOG.md 2026-10-25 (110)). A range found complete
* gets stored_at and isn't read again.
*/
private async corpusTargets(rows: (q: any) => any, taken: Set<number>): Promise<Target[]> {
const { dir, ahead } = coordinatorConfig.corpus
if (!dir || ahead <= 0) return []
const { perRange, perGroup } = coordinatorConfig.spool
const ofGroup =
perGroup > 0 && perRange > 0 ? Math.max(1, Math.floor(perGroup / perRange)) : Infinity
const groups = new Map<string, number>()
const candidates = await rows(db.query())
.where('r.capture', true)
// A group taken off the list (groups.active) isn't worth the connections.
.where('g.active', true)
.whereNull('r.stored_at')
.where((q: any) =>
q
.where((p: any) => p.where('r.status', 'planned').where('r.spooled_chunks', 0))
.orWhere('r.status', 'done')
)
.orderByRaw('r.priority, row_number() OVER (PARTITION BY r.group_id ORDER BY r.id), r.id')
.limit(ahead * 16)
const targets: Target[] = []
for (const row of candidates) {
if (targets.length >= ahead) break
const id = Number(row.id)
if (taken.has(id) || this.stored.has(id)) continue
if ((groups.get(row.group) ?? 0) >= ofGroup) continue
const start = Number(row.start_id)
const end = Number(row.end_id)
const range = { group: row.group, start, end }
if (await Corpus.complete(range)) {
this.stored.add(id)
await db.from('ranges').where('id', id).update({ stored_at: new Date() })
continue
}
const chunks = Spool.chunksOf({ start, end })
const missing: ChunkSpan[] = []
for (const span of chunks)
if (!this.claimed.has(`${id}:${span.from}`) && !(await Corpus.has(range, span)))
missing.push(span)
if (missing.length > 0) {
targets.push({
id,
group: row.group,
plain: new Set((row.plain_chunks ?? []).map(Number)),
missing,
total: chunks.length,
start,
end,
capture: true,
corpusOnly: true,
})
groups.set(row.group, (groups.get(row.group) ?? 0) + 1)
}
}
return targets
}
}