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table cache: use a long-lived ReaderProvider
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An `sstable.ReaderProvider` is necessary whenever an sstable has value
blocks. Currently, we allocate one every time we create a point
iterator.

This commit makes the `tableCacheShardReaderProvider` usable in
parallel and maintains a long-lived instance in the `tableCacheValue`.
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@RaduBerinde
RaduBerinde committed Nov 12, 2024
1 parent 9f68a21 commit 048f275
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Showing 3 changed files with 85 additions and 47 deletions.
112 changes: 75 additions & 37 deletions table_cache.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -557,10 +557,6 @@ func (c *tableCacheShard) newPointIter(
if err != nil {
return nil, err
}
var rp sstable.ReaderProvider
if tableFormat >= sstable.TableFormatPebblev3 && v.reader.Properties.NumValueBlocks > 0 {
rp = &tableCacheShardReaderProvider{c: c, file: file, dbOpts: dbOpts}
}

if v.isShared && file.SyntheticSeqNum() != 0 {
if tableFormat < sstable.TableFormatPebblev4 {
Expand All @@ -577,11 +573,11 @@ func (c *tableCacheShard) newPointIter(
uint64(uintptr(unsafe.Pointer(v.reader))), opts.Category)
}
if internalOpts.compaction {
iter, err = cr.NewCompactionIter(transforms, iterStatsAccum, rp, internalOpts.bufferPool)
iter, err = cr.NewCompactionIter(transforms, iterStatsAccum, &v.readerProvider, internalOpts.bufferPool)
} else {
iter, err = cr.NewPointIter(
ctx, transforms, opts.GetLowerBound(), opts.GetUpperBound(), filterer, filterBlockSizeLimit,
internalOpts.stats, iterStatsAccum, rp)
internalOpts.stats, iterStatsAccum, &v.readerProvider)
}
if err != nil {
return nil, err
Expand Down Expand Up @@ -652,15 +648,36 @@ func (c *tableCacheShard) newRangeKeyIter(
return cr.NewRawRangeKeyIter(ctx, transforms)
}

// tableCacheShardReaderProvider implements sstable.ReaderProvider for a
// specific table.
type tableCacheShardReaderProvider struct {
c *tableCacheShard
file *manifest.FileMetadata
dbOpts *tableCacheOpts
v *tableCacheValue
c *tableCacheShard
dbOpts *tableCacheOpts
backingFileNum base.DiskFileNum

mu struct {
sync.Mutex
// v is the result of findNode. Whenever it is not null, we hold a refcount
// on the tableCacheValue.
v *tableCacheValue
// refCount is the number of GetReader() calls that have not received a
// corresponding Close().
refCount int
}
}

var _ sstable.ReaderProvider = &tableCacheShardReaderProvider{}

func (rp *tableCacheShardReaderProvider) init(
c *tableCacheShard, dbOpts *tableCacheOpts, backingFileNum base.DiskFileNum,
) {
rp.c = c
rp.dbOpts = dbOpts
rp.backingFileNum = backingFileNum
rp.mu.v = nil
rp.mu.refCount = 0
}

// GetReader implements sstable.ReaderProvider. Note that it is not the
// responsibility of tableCacheShardReaderProvider to ensure that the file
// continues to exist. The ReaderProvider is used in iterators where the
Expand All @@ -676,21 +693,41 @@ var _ sstable.ReaderProvider = &tableCacheShardReaderProvider{}
// TODO(bananabrick): We could return a wrapper over the Reader to ensure
// that the reader isn't used for other purposes.
func (rp *tableCacheShardReaderProvider) GetReader(ctx context.Context) (*sstable.Reader, error) {
// Calling findNode gives us the responsibility of decrementing v's
// refCount.
v := rp.c.findNode(ctx, rp.file.FileBacking, rp.dbOpts)
rp.mu.Lock()
defer rp.mu.Unlock()

if rp.mu.v != nil {
rp.mu.refCount++
return rp.mu.v.reader, nil
}

// Calling findNodeInternal gives us the responsibility of decrementing v's
// refCount. Note that if the table is no longer in the cache,
// findNodeInternal will need to do IO to initialize a new Reader. We hold
// rp.mu during this time so that concurrent GetReader calls block until the
// Reader is created.
v := rp.c.findNodeInternal(ctx, rp.backingFileNum, rp.dbOpts)
if v.err != nil {
defer rp.c.unrefValue(v)
return nil, v.err
}
rp.v = v
rp.mu.v = v
rp.mu.refCount = 1
return v.reader, nil
}

// Close implements sstable.ReaderProvider.
func (rp *tableCacheShardReaderProvider) Close() {
rp.c.unrefValue(rp.v)
rp.v = nil
rp.mu.Lock()
defer rp.mu.Unlock()
rp.mu.refCount--
if rp.mu.refCount <= 0 {
if rp.mu.refCount < 0 {
panic("pebble: sstable.ReaderProvider misuse")
}
rp.c.unrefValue(rp.mu.v)
rp.mu.v = nil
}
}

// getTableProperties return sst table properties for target file
Expand Down Expand Up @@ -782,20 +819,18 @@ func (c *tableCacheShard) findNode(
// Caution! Here fileMetadata can be a physical or virtual table. Table cache
// readers are associated with the physical backings. All virtual tables with
// the same backing will use the same reader from the cache; so no information
// that can differ among these virtual tables can be plumbed into loadInfo.
info := loadInfo{
backingFileNum: b.DiskFileNum,
}
// that can differ among these virtual tables can be passed to findNodeInternal.
backingFileNum := b.DiskFileNum

return c.findNodeInternal(ctx, info, dbOpts)
return c.findNodeInternal(ctx, backingFileNum, dbOpts)
}

func (c *tableCacheShard) findNodeInternal(
ctx context.Context, loadInfo loadInfo, dbOpts *tableCacheOpts,
ctx context.Context, backingFileNum base.DiskFileNum, dbOpts *tableCacheOpts,
) *tableCacheValue {
// Fast-path for a hit in the cache.
c.mu.RLock()
key := tableCacheKey{dbOpts.cacheID, loadInfo.backingFileNum}
key := tableCacheKey{dbOpts.cacheID, backingFileNum}
if n := c.mu.nodes[key]; n != nil && n.value != nil {
// Fast-path hit.
//
Expand All @@ -817,7 +852,7 @@ func (c *tableCacheShard) findNodeInternal(
case n == nil:
// Slow-path miss of a non-existent node.
n = &tableCacheNode{
fileNum: loadInfo.backingFileNum,
fileNum: backingFileNum,
ptype: tableCacheNodeCold,
}
c.addNode(n, dbOpts)
Expand Down Expand Up @@ -854,6 +889,7 @@ func (c *tableCacheShard) findNodeInternal(
v := &tableCacheValue{
loaded: make(chan struct{}),
}
v.readerProvider.init(c, dbOpts, backingFileNum)
v.refCount.Store(2)
// Cache the closure invoked when an iterator is closed. This avoids an
// allocation on every call to newIters.
Expand All @@ -875,7 +911,7 @@ func (c *tableCacheShard) findNodeInternal(
// Note adding to the cache lists must complete before we begin loading the
// table as a failure during load will result in the node being unlinked.
pprof.Do(context.Background(), tableCacheLabels, func(context.Context) {
v.load(ctx, loadInfo, c, dbOpts)
v.load(ctx, backingFileNum, c, dbOpts)
})
return v
}
Expand Down Expand Up @@ -1094,51 +1130,53 @@ type tableCacheValue struct {
closeHook func(i sstable.Iterator) error
reader *sstable.Reader
err error
isShared bool
loaded chan struct{}
// Reference count for the value. The reader is closed when the reference
// count drops to zero.
refCount atomic.Int32
}

// loadInfo contains the information needed to populate a new cache entry.
type loadInfo struct {
backingFileNum base.DiskFileNum
isShared bool

// readerProvider is embedded here so that we only allocate it once as long as
// the table stays in the cache. Its state is not always logically tied to
// this specific tableCacheValue - if a table goes out of the cache and then
// comes back in, the readerProvider in a now-defunct tableCacheValue can
// still be used and will internally refer to the new tableCacheValue.
readerProvider tableCacheShardReaderProvider
}

func (v *tableCacheValue) load(
ctx context.Context, loadInfo loadInfo, c *tableCacheShard, dbOpts *tableCacheOpts,
ctx context.Context, backingFileNum base.DiskFileNum, c *tableCacheShard, dbOpts *tableCacheOpts,
) {
// Try opening the file first.
var f objstorage.Readable
var err error
f, err = dbOpts.objProvider.OpenForReading(
ctx, fileTypeTable, loadInfo.backingFileNum, objstorage.OpenOptions{MustExist: true},
ctx, fileTypeTable, backingFileNum, objstorage.OpenOptions{MustExist: true},
)
if err == nil {
o := dbOpts.readerOpts
o.SetInternalCacheOpts(sstableinternal.CacheOptions{
Cache: dbOpts.cache,
CacheID: dbOpts.cacheID,
FileNum: loadInfo.backingFileNum,
FileNum: backingFileNum,
})
v.reader, err = sstable.NewReader(ctx, f, o)
}
if err == nil {
var objMeta objstorage.ObjectMetadata
objMeta, err = dbOpts.objProvider.Lookup(fileTypeTable, loadInfo.backingFileNum)
objMeta, err = dbOpts.objProvider.Lookup(fileTypeTable, backingFileNum)
v.isShared = objMeta.IsShared()
}
if err != nil {
v.err = errors.Wrapf(
err, "pebble: backing file %s error", loadInfo.backingFileNum)
err, "pebble: backing file %s error", backingFileNum)
}
if v.err != nil {
c.mu.Lock()
defer c.mu.Unlock()
// Lookup the node in the cache again as it might have already been
// removed.
key := tableCacheKey{dbOpts.cacheID, loadInfo.backingFileNum}
key := tableCacheKey{dbOpts.cacheID, backingFileNum}
n := c.mu.nodes[key]
if n != nil && n.value == v {
c.releaseNode(n)
Expand Down
2 changes: 1 addition & 1 deletion testdata/ingest
View file
Original file line number Diff line number Diff line change
Expand Up @@ -54,7 +54,7 @@ Virtual tables: 0 (0B)
Local tables size: 569B
Compression types: snappy: 1
Block cache: 3 entries (1.1KB) hit rate: 18.2%
Table cache: 1 entries (864B) hit rate: 50.0%
Table cache: 1 entries (904B) hit rate: 50.0%
Secondary cache: 0 entries (0B) hit rate: 0.0%
Snapshots: 0 earliest seq num: 0
Table iters: 0
Expand Down
18 changes: 9 additions & 9 deletions testdata/metrics
View file
Original file line number Diff line number Diff line change
Expand Up @@ -76,7 +76,7 @@ Virtual tables: 0 (0B)
Local tables size: 589B
Compression types: snappy: 1
Block cache: 2 entries (716B) hit rate: 0.0%
Table cache: 1 entries (864B) hit rate: 0.0%
Table cache: 1 entries (904B) hit rate: 0.0%
Secondary cache: 0 entries (0B) hit rate: 0.0%
Snapshots: 0 earliest seq num: 0
Table iters: 1
Expand Down Expand Up @@ -136,7 +136,7 @@ Virtual tables: 0 (0B)
Local tables size: 595B
Compression types: snappy: 1
Block cache: 2 entries (716B) hit rate: 33.3%
Table cache: 2 entries (1.7KB) hit rate: 66.7%
Table cache: 2 entries (1.8KB) hit rate: 66.7%
Secondary cache: 0 entries (0B) hit rate: 0.0%
Snapshots: 0 earliest seq num: 0
Table iters: 2
Expand Down Expand Up @@ -183,7 +183,7 @@ Virtual tables: 0 (0B)
Local tables size: 595B
Compression types: snappy: 1
Block cache: 2 entries (716B) hit rate: 33.3%
Table cache: 2 entries (1.7KB) hit rate: 66.7%
Table cache: 2 entries (1.8KB) hit rate: 66.7%
Secondary cache: 0 entries (0B) hit rate: 0.0%
Snapshots: 0 earliest seq num: 0
Table iters: 2
Expand Down Expand Up @@ -227,7 +227,7 @@ Virtual tables: 0 (0B)
Local tables size: 595B
Compression types: snappy: 1
Block cache: 2 entries (716B) hit rate: 33.3%
Table cache: 1 entries (864B) hit rate: 66.7%
Table cache: 1 entries (904B) hit rate: 66.7%
Secondary cache: 0 entries (0B) hit rate: 0.0%
Snapshots: 0 earliest seq num: 0
Table iters: 1
Expand Down Expand Up @@ -510,7 +510,7 @@ Virtual tables: 0 (0B)
Local tables size: 4.3KB
Compression types: snappy: 7
Block cache: 8 entries (2.8KB) hit rate: 9.1%
Table cache: 1 entries (864B) hit rate: 53.8%
Table cache: 1 entries (904B) hit rate: 53.8%
Secondary cache: 0 entries (0B) hit rate: 0.0%
Snapshots: 0 earliest seq num: 0
Table iters: 0
Expand Down Expand Up @@ -575,7 +575,7 @@ Virtual tables: 0 (0B)
Local tables size: 6.1KB
Compression types: snappy: 10
Block cache: 8 entries (2.8KB) hit rate: 9.1%
Table cache: 1 entries (864B) hit rate: 53.8%
Table cache: 1 entries (904B) hit rate: 53.8%
Secondary cache: 0 entries (0B) hit rate: 0.0%
Snapshots: 0 earliest seq num: 0
Table iters: 0
Expand Down Expand Up @@ -853,7 +853,7 @@ Virtual tables: 0 (0B)
Local tables size: 0B
Compression types: snappy: 1
Block cache: 0 entries (0B) hit rate: 0.0%
Table cache: 1 entries (864B) hit rate: 0.0%
Table cache: 1 entries (904B) hit rate: 0.0%
Secondary cache: 0 entries (0B) hit rate: 0.0%
Snapshots: 0 earliest seq num: 0
Table iters: 0
Expand Down Expand Up @@ -901,7 +901,7 @@ Virtual tables: 0 (0B)
Local tables size: 0B
Compression types: snappy: 2
Block cache: 4 entries (1.4KB) hit rate: 0.0%
Table cache: 1 entries (864B) hit rate: 50.0%
Table cache: 1 entries (904B) hit rate: 50.0%
Secondary cache: 0 entries (0B) hit rate: 0.0%
Snapshots: 0 earliest seq num: 0
Table iters: 0
Expand Down Expand Up @@ -950,7 +950,7 @@ Virtual tables: 0 (0B)
Local tables size: 589B
Compression types: snappy: 3
Block cache: 4 entries (1.4KB) hit rate: 0.0%
Table cache: 1 entries (864B) hit rate: 50.0%
Table cache: 1 entries (904B) hit rate: 50.0%
Secondary cache: 0 entries (0B) hit rate: 0.0%
Snapshots: 0 earliest seq num: 0
Table iters: 0
Expand Down

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