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mergewriter.go
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mergewriter.go
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package splitmerge
import (
"io"
"github.com/T0n0T/wal-g/utility"
"github.com/wal-g/tracelog"
)
// MergeWriter returns list of WriteCloser-s
// Then it reads data from each of n=`parts` WriteClosers in blocks of `blockSize` and writes data to `sink` writer.
// MergeWriter gets ownership over sink and will close it.
func MergeWriter(sink io.WriteCloser, parts int, blockSize int) []io.WriteCloser {
result := make([]io.WriteCloser, 0)
channels := make([]chan []byte, 0)
writeResults := make([]chan writeResult, 0)
sink = &utility.CloseOnce{WriteCloser: sink}
for i := 0; i < parts; i++ {
channels = append(channels, make(chan []byte))
writeResults = append(writeResults, make(chan writeResult))
cw := newChannelWriter(channels[i], writeResults[i])
fbsw := newFixedBlockSizeWriter(cw, blockSize)
result = append(result, fbsw)
}
// start MergeWriter:
go func() {
defer (func() {
for _, wrch := range writeResults {
close(wrch)
}
})()
for {
closed := 0
for i, ch := range channels {
block, ok := <-ch
if !ok {
tracelog.DebugLogger.Printf("MergeWriter. #%d closed", i)
closed++
continue
}
rbytes := len(block)
wbytes, err := sink.Write(block)
writeResults[i] <- writeResult{n: wbytes, err: err}
if wbytes != rbytes {
tracelog.DebugLogger.Printf("%d / %d bytes written due to %v", wbytes, rbytes, err)
}
if err != nil {
tracelog.ErrorLogger.Printf("MergeWriter error: %v", err)
// It is unrecoverable error - close sink. All consequent writes will return error.
// This will ensure that all channels will be gracefully closed
err = sink.Close()
if err != nil {
tracelog.ErrorLogger.Printf("MergeWriter error on sink close: %v", err)
}
continue
}
}
if closed == len(channels) {
tracelog.DebugLogger.Printf("MergeWriter: finished")
err := sink.Close()
if err != nil {
tracelog.ErrorLogger.Printf("MergeWriter error on sink close: %v", err)
}
return
}
}
}()
return result
}