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first look at making region writes reuse old space

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This commit is contained in:
Dylan K. Taylor
2020-06-15 18:36:54 +01:00
parent da42c8d020
commit 6a7b77fee2
3 changed files with 200 additions and 10 deletions
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52
src/pocketmine/level/format/io/region/RegionLoader.php
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@ -65,7 +65,7 @@ class RegionLoader{
public const MAX_SECTOR_LENGTH = 255 << 12; //255 sectors (~0.996 MiB)
public const REGION_HEADER_LENGTH = 8192; //4096 location table + 4096 timestamps
private const FIRST_SECTOR = 2; //location table occupies 0 and 1
public const FIRST_SECTOR = 2; //location table occupies 0 and 1
/** @var int */
public static $COMPRESSION_LEVEL = 7;
@ -82,6 +82,8 @@ class RegionLoader{
protected $nextSector = self::FIRST_SECTOR;
/** @var RegionLocationTableEntry[]|null[] */
protected $locationTable = [];
/** @var RegionGarbageMap */
protected $garbageTable;
/** @var int */
public $lastUsed = 0;
@ -89,6 +91,7 @@ class RegionLoader{
$this->x = $regionX;
$this->z = $regionZ;
$this->filePath = $filePath;
$this->garbageTable = new RegionGarbageMap([]);
}
/**
@ -199,18 +202,49 @@ class RegionLoader{
$newSize = (int) ceil(($length + 4) / 4096);
$index = self::getChunkOffset($x, $z);
if($this->locationTable[$index] === null or $this->locationTable[$index]->getSectorCount() < $newSize){
$offset = $this->nextSector;
}else{
$offset = $this->locationTable[$index]->getFirstSector(); //reuse old location - TODO: risk of corruption during power failure
/*
* look for an unused area big enough to hold this data
* this is corruption-resistant (it leaves the old data intact if a failure occurs when writing new data), and
* also allows the file to become more compact across consecutive writes without introducing a dedicated garbage
* collection mechanism.
*/
$newLocation = $this->garbageTable->allocate($newSize);
/* if no gaps big enough were found, append to the end of the file instead */
if($newLocation === null){
$newLocation = new RegionLocationTableEntry($this->nextSector, $newSize, time());
$this->bumpNextFreeSector($newLocation);
}
$this->bumpNextFreeSector($this->locationTable[$index] = new RegionLocationTableEntry($offset, $newSize, time()));
fseek($this->filePointer, $offset << 12);
/* write the chunk data into the chosen location */
fseek($this->filePointer, $newLocation->getFirstSector() << 12);
fwrite($this->filePointer, str_pad(Binary::writeInt($length) . chr(self::COMPRESSION_ZLIB) . $chunkData, $newSize << 12, "\x00", STR_PAD_RIGHT));
/*
* update the file header - we do this after writing the main data, so that if a failure occurs while writing,
* the header will still point to the old (intact) copy of the chunk, instead of a potentially broken new
* version of the file (e.g. partially written).
*/
$oldLocation = $this->locationTable[$index];
$this->locationTable[$index] = $newLocation;
$this->writeLocationIndex($index);
if($oldLocation !== null){
/* release the area containing the old copy to the garbage pool */
$this->garbageTable->add($oldLocation);
$endGarbage = $this->garbageTable->end();
$nextSector = $this->nextSector;
for(; $endGarbage !== null and $endGarbage->getLastSector() + 1 === $nextSector; $endGarbage = $this->garbageTable->end()){
$nextSector = $endGarbage->getFirstSector();
$this->garbageTable->remove($endGarbage);
}
if($nextSector !== $this->nextSector){
$this->nextSector = $nextSector;
ftruncate($this->filePointer, $this->nextSector << 12);
}
}
}
/**
@ -289,6 +323,8 @@ class RegionLoader{
$this->checkLocationTableValidity();
$this->garbageTable = RegionGarbageMap::buildFromLocationTable($this->locationTable);
fseek($this->filePointer, 0);
}