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use super::{increment_bytes, partition_for_key, Result, DB};
use crate::memtable::Entry;
use crate::sstable::{SSTable, FLAG_INLINE, FLAG_MERGE, FLAG_POINTER, FLAG_TOMBSTONE};
use crate::types::InternalKey;
use crate::vlog::VLog;
use bytes::Bytes;
use std::path::PathBuf;
use std::sync::{Arc, Mutex};
use std::time::Instant;
impl DB {
/// Get an `SSTable` handle, loading from disk if not cached.
///
/// This is the canonical way to access `SSTables` for reads. Uses a cache-aside
/// pattern: check cache first, load on miss.
///
/// # Caching behavior
/// - Cache hit: Returns cached `Arc<Mutex<SSTable>>` (fast path)
/// - Cache miss: Opens `SSTable`, configures buffer pool/`vLog`, caches it
///
/// # Thread safety
/// The returned handle is wrapped in `Arc<Mutex<>>` for safe concurrent access.
/// Multiple readers can hold references; the mutex serializes actual I/O.
fn get_sstable(&self, path: &PathBuf) -> Result<Arc<Mutex<SSTable>>> {
self.sstable_cache.get_or_insert_with(path, || {
let has_vlog = self.has_vlog.load(std::sync::atomic::Ordering::Relaxed);
// Choose caching strategy: buffer pool (if configured) or global block cache
let mut sstable = if let Some(ref pool) = self.buffer_pool {
SSTable::open_with_buffer_pool(path, Some(Arc::clone(pool)))?
} else {
let global_cache = Some(Arc::clone(&self.global_block_cache));
SSTable::open_with_global_cache(path, global_cache)?
};
// Attach vLog for value separation if enabled
if has_vlog {
let vlog_path = self.options.data_dir.join("values.vlog");
sstable = sstable.with_vlog(VLog::open(&vlog_path)?);
}
Ok(Arc::new(Mutex::new(sstable)))
})
}
/// Get a value by key.
///
/// Returns the value if found, `None` if the key doesn't exist or was deleted.
/// Automatically handles merge operations if a merge operator is configured.
pub fn get(&self, key: impl AsRef<[u8]>) -> Result<Option<Bytes>> {
let start = if self.options.disable_metrics {
None
} else {
Some(Instant::now())
};
let key = key.as_ref();
self.read_count
.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
// Lazy-init operands only when merge ops are encountered (rare case)
let mut operands: Option<Vec<Bytes>> = None;
// 1. Check correct partition first
let partition = partition_for_key(key);
let mt = self.memtables[partition].load();
if let Some(entry) = mt.get_entry(key) {
match entry {
Entry::Value(v) => {
return Ok(self.resolve_merge_opt(key, Some(v), &operands, start))
}
Entry::Tombstone => return Ok(self.resolve_merge_opt(key, None, &operands, start)),
Entry::Merge {
base: Some(v),
operands: ops,
} => {
// Found base in memtable - resolve immediately
operands.get_or_insert_with(Vec::new).extend(ops);
return Ok(self.resolve_merge_opt(key, Some(v), &operands, start));
}
Entry::Merge {
base: None,
operands: ops,
} => {
// No base yet - continue searching
operands.get_or_insert_with(Vec::new).extend(ops);
}
}
}
// 2. Check immutable partitions
let immut_arc = self.immutable_memtables.load();
if let Some(ref immutable_partitions) = **immut_arc {
let partition_mt = &immutable_partitions[partition];
if let Some(entry) = partition_mt.get_entry(key) {
match entry {
Entry::Value(v) => {
return Ok(self.resolve_merge_opt(key, Some(v), &operands, start))
}
Entry::Tombstone => {
return Ok(self.resolve_merge_opt(key, None, &operands, start))
}
Entry::Merge {
base: Some(v),
operands: ops,
} => {
operands.get_or_insert_with(Vec::new).extend(ops);
return Ok(self.resolve_merge_opt(key, Some(v), &operands, start));
}
Entry::Merge {
base: None,
operands: ops,
} => {
operands.get_or_insert_with(Vec::new).extend(ops);
}
}
}
}
// 3. Check SSTables in LSM tree
let lsm_arc = self.lsm.load();
for level_num in 0..lsm_arc.num_levels() {
if let Some(level) = lsm_arc.level(level_num) {
// Iterate directly in reverse - no Vec allocation needed
for sstable_path in level.sstables().iter().rev() {
let cached_sstable = self.get_sstable(sstable_path)?;
let mut sstable = cached_sstable.lock().expect("SSTable lock poisoned");
let result = sstable.get_entry_mvcc(key, u64::MAX)?;
if let Some((data, flag)) = result {
match flag {
FLAG_INLINE | FLAG_POINTER => {
return Ok(self.resolve_merge_opt(
key,
Some(data),
&operands,
start,
));
}
FLAG_TOMBSTONE => {
return Ok(self.resolve_merge_opt(key, None, &operands, start));
}
FLAG_MERGE => {
let end_key_vec = increment_bytes(key);
let end_key_slice = end_key_vec.as_deref();
let iter = sstable.scan_range(key, end_key_slice);
for (k, entry) in iter.flatten() {
if k == key {
match entry {
Entry::Value(v) => {
return Ok(self.resolve_merge_opt(
key,
Some(v),
&operands,
start,
));
}
Entry::Merge {
base,
operands: ops,
} => {
operands.get_or_insert_with(Vec::new).extend(ops);
if let Some(v) = base {
return Ok(self.resolve_merge_opt(
key,
Some(v),
&operands,
start,
));
}
}
Entry::Tombstone => {
return Ok(self.resolve_merge_opt(
key, None, &operands, start,
));
}
}
}
}
}
_ => return Err(crate::sstable::SSTableError::InvalidFormat.into()),
}
}
}
}
}
Ok(self.resolve_merge_opt(key, None, &operands, start))
}
/// Get a value at a specific sequence number (snapshot isolation).
pub(crate) fn get_at_seq(&self, key: &[u8], snapshot_seq: u64) -> Result<Option<Bytes>> {
let partition = partition_for_key(key);
let mt = self.memtables[partition].load();
if let Some((value, _seq)) = mt.get(key, snapshot_seq) {
if value.is_empty() {
return Ok(None);
}
return Ok(Some(value));
}
let immut_arc = self.immutable_memtables.load();
if let Some(ref immutable_partitions) = **immut_arc {
let partition_mt = &immutable_partitions[partition];
if let Some((value, _seq)) = partition_mt.get(key, snapshot_seq) {
if value.is_empty() {
return Ok(None);
}
return Ok(Some(value));
}
}
let lsm_arc = self.lsm.load();
for level_num in 0..lsm_arc.num_levels() {
if let Some(level) = lsm_arc.level(level_num) {
for sstable_path in level.sstables().iter().rev() {
let cached_sstable = self.get_sstable(sstable_path)?;
let mut sstable = cached_sstable.lock().expect("SSTable lock poisoned");
if let Ok(Some(value)) = sstable.get_mvcc(key, snapshot_seq) {
if value.is_empty() {
return Ok(None);
}
return Ok(Some(value));
}
}
}
}
Ok(None)
}
/// Get the latest sequence number for a key.
pub(crate) fn get_latest_seq(&self, key: &[u8]) -> Result<Option<u64>> {
let partition = partition_for_key(key);
let mt = self.memtables[partition].load();
if let Some((_value, seq)) = mt.get(key, u64::MAX) {
return Ok(Some(seq));
}
let immut_arc = self.immutable_memtables.load();
if let Some(ref immutable_partitions) = **immut_arc {
let partition_mt = &immutable_partitions[partition];
if let Some((_value, seq)) = partition_mt.get(key, u64::MAX) {
return Ok(Some(seq));
}
}
let lsm_arc = self.lsm.load();
for level_num in 0..lsm_arc.num_levels() {
if let Some(level) = lsm_arc.level(level_num) {
for sstable_path in level.sstables().iter().rev() {
let cached_sstable = self.get_sstable(sstable_path)?;
let mut sstable = cached_sstable.lock().expect("SSTable lock poisoned");
if let Ok(Some((encoded_key, _value))) = sstable.get_raw_entry(key) {
if let Some(ikey) = InternalKey::decode(encoded_key) {
return Ok(Some(ikey.seq));
}
}
}
}
}
Ok(None)
}
/// Resolve merge with Option<Vec<Bytes>> - avoids allocation when no merges
#[inline]
pub(crate) fn resolve_merge_opt(
&self,
key: &[u8],
base: Option<Bytes>,
operands: &Option<Vec<Bytes>>,
start: Option<Instant>,
) -> Option<Bytes> {
match operands {
None => {
// Fast path: no merge operands (common case)
if let Some(s) = start {
self.metrics.record_get(s.elapsed());
}
base
}
Some(ops) if ops.is_empty() => {
if let Some(s) = start {
self.metrics.record_get(s.elapsed());
}
base
}
Some(ops) => self.resolve_merge(key, base, ops, start),
}
}
pub(crate) fn resolve_merge(
&self,
key: &[u8],
base: Option<Bytes>,
operands: &[Bytes],
start: Option<Instant>,
) -> Option<Bytes> {
if operands.is_empty() {
if let Some(s) = start {
self.metrics.record_get(s.elapsed());
}
return base;
}
if let Some(ref op) = self.options.merge_operator {
let ops_reversed: Vec<&[u8]> = operands
.iter()
.rev()
.map(std::convert::AsRef::as_ref)
.collect();
let base_slice = base.as_ref().map(std::convert::AsRef::as_ref);
let result = if let Some(merged) = op.full_merge(key, base_slice, &ops_reversed) {
Some(Bytes::from(merged))
} else {
base
};
if let Some(s) = start {
self.metrics.record_get(s.elapsed());
}
result
} else {
if let Some(s) = start {
self.metrics.record_get(s.elapsed());
}
base
}
}
}