Baguette/dodb.cr
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Documentation, a few implementations rewritten, make source more consistent.

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This commit is contained in:
Philippe PITTOLI 2024-05-20 13:10:17 +02:00
parent 39b427886f
commit df705543b6
7 changed files with 568 additions and 563 deletions
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2
Makefile
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@ -17,7 +17,7 @@ release:
make build OPTS="--release --progress"
doc:
crystal docs
crystal docs src/dodb.cr
HTTPD_ACCESS_LOGS ?= /tmp/access-dodb-docs.log
HTTPD_ADDR ?= 127.0.0.1

78
src/cached.cr
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@ -1,7 +1,3 @@
require "file_utils"
require "json"
require "./dodb.cr"
class Hash(K,V)
def reverse
rev = Array(Tuple(K,V)).new
@ -17,6 +13,9 @@ class Hash(K,V)
end
end
# Cached database, stores data on the file-system and keeps it in RAM.
#
# WARNING: beware of the RAM use, see `DODB::StackedDataBase` for a less memory-hungry option.
class DODB::CachedDataBase(V) < DODB::Storage(V)
@indexers = [] of Indexer(V)
property data = Hash(Int32, V).new
@ -82,6 +81,16 @@ class DODB::CachedDataBase(V) < DODB::Storage(V)
@data[key] = value
end
# :inherit:
#
# As `DODB::Storage#each_key`, keys are sorted in order to keep the behavior consistent.
private def each_key(reversed : Bool = false)
keys = @data.keys.sort
(reversed ? keys.reverse : keys).each do |key|
yield key
end
end
# :inherit:
def each_with_key(reversed : Bool = false, offset = 0, limit : Int32? = -1)
limit = if l = limit
@ -122,64 +131,3 @@ class DODB::CachedDataBase(V) < DODB::Storage(V)
@data = Hash(Int32, V).new
end
end
# `DODB::RAMOnlyDataBase` is a database without a file-system representation,
# enabling the use of DODB to store data which have the same lifetime as the application.
# Indexing (indexes, partitions, tags) will behave the same way.
class DODB::RAMOnlyDataBase(V) < DODB::CachedDataBase(V)
# Initialization still uses a directory name and creates a few paths.
# This is an implementation detail to re-use code of `DODB::Storage` and to get the indexers to work.
def initialize(@directory_name : String)
Dir.mkdir_p data_path
Dir.mkdir_p locks_directory
@last_key = -1
end
# The `last_key` function doesn't read a file in the `DODB::RAMOnlyDataBase` database.
def last_key
@last_key
end
# The `last_key=` function doesn't write to a file in the `DODB::RAMOnlyDataBase` database.
def last_key=(key : Int32)
@last_key = key
end
# WARNING: takes `[]?` and `[]` implementations from `CachedDataBase`.
# This will lead to errors in case the implementations change, be aware.
def []=(key : Int32, value : V)
old_value = self.[key]?
check_collisions! key, value, old_value
# Removes any old indices or partitions pointing to a value about to be replaced.
if old_value
remove_indexes key, old_value
end
write_indexes key, value
if key > last_key
self.last_key = key
end
@data[key] = value
end
# :inherit:
def unsafe_delete(key : Int32)
value = self[key]?
return if value.nil?
remove_indexes key, value
@data.delete key
value
end
private def remove_data!
super
@data = Hash(Int32, V).new
end
end

503
src/dodb.cr
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@ -1,501 +1,10 @@
require "file_utils"
require "json"
require "./dodb/*"
require "./dodb/*" # Indexes (basic indexes, partitions, tags, etc.).
# The `DODB::Storage` abstract class defines the specifications of
# subsequent DODB databases (uncached, cached, RAM-only, etc.).
abstract class DODB::Storage(V)
property directory_name : String
# A DODB database is instanciated with a *path* where data will be written.
def initialize(@directory_name : String)
end
# Requests a (named) lock.
# Locks prevent concurrent access to the same data.
#
# In case of a request for a lock that is already in use,
# wait for a millisecond then retry, loop until it works.
# A lock is simply an opened file with the `LibC::O_EXCL` flag.
def request_lock(name, subname = nil)
r = -1
file_path = get_lock_file_path name, subname
file_perms = 0o644
flags = LibC::O_EXCL | LibC::O_CREAT
while (r = LibC.open file_path, flags, file_perms) == -1
sleep 1.milliseconds
end
LibC.close r
end
# Releases a (named) lock.
#
# The implementation is simple, it just removes the file.
def release_lock(name, subname = nil)
File.delete get_lock_file_path name, subname
end
private def key_file
"#{@directory_name}/last-key"
end
# Reads the last *key* in the database.
def last_key : Int32
File.read(key_file).to_i
end
# Changes the last *key* in the database.
def last_key=(x : Int32)
file = File.open(key_file, "w")
file << x.to_s
file.close
x
rescue
raise Exception.new "could not update last-key file"
end
# Take a database key and convert it in a formated string. Example: 343 -> "0000000343"
def stringify_key(key : Int32)
# Negative numbers give strange results with Crystal’s printf.
if key >= 0
"%010i" % key
else
key.to_s
end
end
# Adds a value to the database without a locking mechanism.
#
# For a thread-safe version, use `#<<`.
#
# WARNING: not thread-safe.
def unsafe_add(item : V)
key = last_key + 1
self[key] = item
self.last_key = key
key # FIXME: Should we really return the internal key?
rescue e
raise e
end
# Adds a value to the database, with a locking mechanism to prevent race conditions.
#
# This operation should be thread-safe since a lock is required before tinkering with the database.
# Because of the file-system operations, this function may be a bit slow.
# For single-thread applications, use the `#unsafe_add` operation instead.
def <<(item : V)
request_lock "key"
key = last_key + 1
self[key] = item
self.last_key = key
release_lock "key"
key # FIXME: Should we really return the internal key?
rescue e
release_lock "key"
raise e
end
# Lists all entries in the database.
#
# WARNING: Very slow. Try not to use.
def each(reversed : Bool = false, offset = 0, limit : Int32? = nil)
each_with_key(
reversed: reversed,
offset: offset,
limit: limit
) do |item, key|
yield item
end
end
# Converts all the database into an array.
#
# WARNING: Very slow. Try not to use.
def to_a(reversed : Bool = false, offset = 0, limit : Int32? = nil)
array = ::Array(V).new
each(
reversed: reversed,
offset: offset,
limit: limit
) do |value|
array << value
end
array
end
# Converts the entire database into a hash.
#
# WARNING: Very slow. Try not to use.
def to_h(reversed : Bool = false, offset = 0, limit : Int32? = nil)
hash = ::Hash(Int32, V).new
each_with_key(
reversed: reversed,
offset: offset,
limit: limit
) do |element, key|
hash[key] = element
end
hash
end
# Writes all indexes (basic indexes, partitions, tags, etc.) for a value.
def write_indexes(key : Int32, value : V)
@indexers.each &.index(stringify_key(key), value)
end
# Creates a new basic index **with a cache**.
# The *name* parameter is the name of the directory that will be created.
def new_index(name : String, &block : Proc(V, String | DODB::NoIndex))
CachedIndex(V).new(self, @directory_name, name, block).tap do |indexer|
@indexers << indexer
end
end
# Creates a new basic index **without a cache**.
# The *name* parameter is the name of the directory that will be created.
#
# NOTE: this will be a lot slower than the cached version.
def new_uncached_index(name : String, &block : Proc(V, String | DODB::NoIndex))
Index(V).new(self, @directory_name, name, block).tap do |indexer|
@indexers << indexer
end
end
# Creates a new basic index **only in RAM**.
# The *name* parameter is the name of the directory that will be created.
#
# NOTE: this index is the fastest, but doesn't have a file-system representation.
def new_RAM_index(name : String, &block : Proc(V, String | DODB::NoIndex))
RAMOnlyIndex(V).new(self, @directory_name, name, block).tap do |indexer|
@indexers << indexer
end
end
# Gets an *index object* based on its name.
def get_index(name : String, key)
index = @indexers.find &.name.==(name)
index.not_nil!.as(DODB::Index).get key
end
# Creates a new partition **with a cache**.
# The *name* parameter is the name of the directory that will be created.
def new_partition(name : String, &block : Proc(V, String | DODB::NoIndex))
CachedPartition(V).new(self, @directory_name, name, block).tap do |table|
@indexers << table
end
end
# Creates a new partition **without a cache**.
# The *name* parameter is the name of the directory that will be created.
#
# NOTE: this will be a lot slower than the cached version.
def new_uncached_partition(name : String, &block : Proc(V, String | DODB::NoIndex))
Partition(V).new(self, @directory_name, name, block).tap do |table|
@indexers << table
end
end
# Creates a new partition **only in RAM**.
# The *name* parameter is the name of the directory that will be created.
#
# NOTE: this partition index is the fastest but doesn't have a file-system representation.
def new_RAM_partition(name : String, &block : Proc(V, String | DODB::NoIndex))
RAMOnlyPartition(V).new(self, @directory_name, name, block).tap do |table|
@indexers << table
end
end
# Gets an *index (partition) object* based on its name.
def get_partition(table_name : String, partition_name : String)
partition = @indexers.find &.name.==(table_name)
partition.not_nil!.as(DODB::Partition).get partition_name
end
# Creates a new tag **with a cache**.
# The *name* parameter is the name of the directory that will be created.
def new_tags(name : String, &block : Proc(V, Array(String) | DODB::NoIndex))
CachedTags(V).new(self, @directory_name, name, block).tap do |tags|
@indexers << tags
end
end
# Creates a new tag **without a cache**.
# The *name* parameter is the name of the directory that will be created.
#
# NOTE: this will be a lot slower than the cached version.
def new_uncached_tags(name : String, &block : Proc(V, Array(String) | DODB::NoIndex))
Tags(V).new(self, @directory_name, name, block).tap do |tags|
@indexers << tags
end
end
# Creates a new partition **only in RAM**.
# The *name* parameter is the name of the directory that will be created.
#
# NOTE: this tag index is the fastest but doesn't have a file-system representation.
def new_RAM_tags(name : String, &block : Proc(V, Array(String) | DODB::NoIndex))
RAMOnlyTags(V).new(self, @directory_name, name, block).tap do |tags|
@indexers << tags
end
end
# Gets an *index (tag) object* based on its name.
def get_tags(name, key : String)
tag = @indexers.find &.name.==(name)
tag.not_nil!.as(DODB::Tags).get name, key
end
# WARNING: directed graphs haven't been reviewed in YEARS. Assume as dead code.
def new_directed_graph(name : String, index : DODB::Index(V), &block : Proc(V, Array(String))) : DirectedGraph(V)
DirectedGraph(V).new(self, @directory_name, index, name, block).tap do |table|
@indexers << table
end
end
# Checks for collisions in the indexes.
def check_collisions!(key : Int32, value : V, old_value : V?)
@indexers.each &.check!(stringify_key(key), value, old_value)
end
# Retrieves a value and remove it from the database.
def pop
request_lock "key"
key = last_key
# Some entries may have been removed. We’ll skip over those.
# Not the most efficient if a large number of indices are empty.
while key >= 0 && self[key]?.nil?
key = key - 1
end
if key < 0
return nil
end
poped = self[key]
self.unsafe_delete key
last_key = key - 1
release_lock "key"
poped
end
private def data_path
"#{@directory_name}/data"
end
private def file_path(key : Int32)
"#{data_path}/%010i" % key
end
private def locks_directory : String
"#{@directory_name}/locks"
end
private def get_lock_file_path(name : String, subname : String? = nil)
if subname
"#{locks_directory}/#{name}-#{subname}.lock" # FIXME: Separator that causes less collisions?
else
"#{locks_directory}/#{name}.lock"
end
end
private def read(file_path : String)
V.from_json ::File.read file_path
end
private def remove_data!
FileUtils.rm_rf data_path
Dir.mkdir_p data_path
end
private def remove_indexing!
@indexers.each do |indexer|
indexer.nuke_index
end
end
# Removes all indices and then rewrites them all.
#
# WARNING: slow operation.
def reindex_everything!
remove_indexing!
each_with_key() do |item, key|
write_indexes key, item
end
end
# Removes all indexes of a value.
def remove_indexes(key : Int32, value : V)
@indexers.each &.deindex(stringify_key(key), value)
end
# Gets the data with the *key*.
# In case the data is missing, returns *nil*.
def []?(key : Int32) : V?
self[key]
rescue MissingEntry
# FIXME: Only rescue JSON and “no such file” errors.
return nil
end
# Gets the data with the *key*.
# In case the data is missing, returns an exception `DODB::MissingEntry`.
abstract def [](key : Int32)
# Replaces the data with the *key*.
# In case the data is missing, returns an exception `DODB::MissingEntry`.
abstract def []=(key : Int32, value : V)
# Deletes the data with the *key* but doesn't request for a lock.
# This function is required since `#pop` is already locked before trying to remove an entry,
# thus calling `#unsafe_delete`.
abstract def unsafe_delete(key : Int32)
# Deletes the data with the *key*.
def delete(key : Int32)
request_lock "key"
value = unsafe_delete key
release_lock "key"
value
end
end
class DODB::DataBase(V) < DODB::Storage(V)
@indexers = [] of Indexer(V)
def initialize(@directory_name : String)
Dir.mkdir_p data_path
Dir.mkdir_p locks_directory
begin
self.last_key
rescue
self.last_key = -1
end
end
def [](key : Int32) : V
raise MissingEntry.new(key) unless ::File.exists? file_path key
read file_path key
end
def []=(key : Int32, value : V)
old_value = self.[key]?
check_collisions! key, value, old_value
# Removes any old indices or partitions pointing to a value about
# to be replaced.
if old_value
remove_indexes key, old_value
end
# Avoids corruption in case the application crashes while writing.
file_path(key).tap do |path|
::File.write "#{path}.new", value.to_json
::FileUtils.mv "#{path}.new", path
end
write_indexes key, value
if key > last_key
self.last_key = key
end
end
# :inherit:
def unsafe_delete(key : Int32)
value = self[key]?
return if value.nil?
begin
::File.delete file_path key
rescue File::NotFoundError
end
remove_indexes key, value
value
end
private def each_key(reversed = false)
start = 0
_end = last_key
step = 1
if reversed
start = _end
_end = 0
step = -1
end
key = start
while step == 1 ? key <= _end : key >= _end
full_path = file_path key
if File.exists? full_path
yield key, full_path
end
key = key + step
end
end
# Lists all database entries with their key.
# Can be useful for making dumps or to restore a database.
#
# WARNING: Very slow. Try not to use.
def each_with_key(reversed : Bool = false, offset = 0, limit : Int32? = -1)
dirname = data_path
limit = if l = limit
l
else
-1
end
each_key(reversed) do |key, path|
offset -= 1 if offset >= 0
next if offset >= 0
return if limit == 0
limit -= 1 if limit > 0
begin
# FIXME: Only intercept JSON parsing errors.
field = read path
rescue
next
end
yield field, key
end
end
end
require "./cached.cr"
require "./storage.cr" # Database specs.
require "./uncached.cr" # Uncached database.
require "./cached.cr" # Cached database.
require "./stacked.cr" # Reasonably cached database.
require "./ramonly.cr" # RAM-only database.

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src/ramonly.cr Normal file
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@ -0,0 +1,60 @@
# `DODB::RAMOnlyDataBase` is a database without a file-system representation,
# enabling the use of DODB to store data which have the same lifetime as the application.
# Indexing (indexes, partitions, tags) will behave the same way.
class DODB::RAMOnlyDataBase(V) < DODB::CachedDataBase(V)
# Initialization still uses a directory name and creates a few paths.
# This is an implementation detail to re-use code of `DODB::Storage` and to get the indexers to work.
def initialize(@directory_name : String)
Dir.mkdir_p data_path
Dir.mkdir_p locks_directory
@last_key = -1
end
# The `last_key` function doesn't read a file in the `DODB::RAMOnlyDataBase` database.
def last_key
@last_key
end
# The `last_key=` function doesn't write to a file in the `DODB::RAMOnlyDataBase` database.
def last_key=(key : Int32)
@last_key = key
end
# WARNING: takes `[]?` and `[]` implementations from `CachedDataBase`.
# This will lead to errors in case the implementations change, be aware.
def []=(key : Int32, value : V)
old_value = self.[key]?
check_collisions! key, value, old_value
# Removes any old indices or partitions pointing to a value about to be replaced.
if old_value
remove_indexes key, old_value
end
write_indexes key, value
if key > last_key
self.last_key = key
end
@data[key] = value
end
# :inherit:
def unsafe_delete(key : Int32)
value = self[key]?
return if value.nil?
remove_indexes key, value
@data.delete key
value
end
private def remove_data!
super
@data = Hash(Int32, V).new
end
end

15
src/stacked.cr Normal file
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@ -0,0 +1,15 @@
# Stacked database: only recently requested entries are kept in memory.
# Most recently used entries are in cache and put on the top of the stack.
# Least recently used entries may be removed from the cache in order to keep the amount of memory used reasonable.
#
# NOTE: fast for frequently requested data and requires a stable (and configurable) amount of memory.
# TODO: not yet implemented.
class DODB::StackedDataBase(V) < DODB::CachedDataBase(V)
# The maximum number of accepted entries in the cache.
property max_entries : Int32
# Initializes the `StackedDataBase` with a maximum number of entries in the cache.
def initialize(directory_name : String, @max_entries : Int32 = 100_000)
super directory_name
end
end

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src/storage.cr Normal file
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@ -0,0 +1,467 @@
# The `DODB::Storage` abstract class defines the specifications of
# subsequent DODB databases (uncached, cached, RAM-only, etc.).
abstract class DODB::Storage(V)
@indexers = [] of Indexer(V)
property directory_name : String
# Creates a database.
#
# A DODB database is instanciated with a *path* where data will be written.
# Another directory is created where locks can be written.
# In case the database is empty, the *last_key* is set to *-1*.
def initialize(@directory_name : String)
Dir.mkdir_p data_path
Dir.mkdir_p locks_directory
begin
self.last_key
rescue
self.last_key = -1
end
end
# Requests a (named) lock.
# Locks prevent concurrent access to the same data.
#
# In case of a request for a lock that is already in use,
# wait for a millisecond then retry, loop until it works.
# A lock is simply an opened file with the `LibC::O_EXCL` flag.
def request_lock(name, subname = nil)
r = -1
file_path = get_lock_file_path name, subname
file_perms = 0o644
flags = LibC::O_EXCL | LibC::O_CREAT
while (r = LibC.open file_path, flags, file_perms) == -1
sleep 1.milliseconds
end
LibC.close r
end
# Releases a (named) lock.
#
# The implementation is simple, it just removes the file.
def release_lock(name, subname = nil)
File.delete get_lock_file_path name, subname
end
private def key_file
"#{@directory_name}/last-key"
end
# Reads the last *key* in the database.
def last_key : Int32
File.read(key_file).to_i
end
# Changes the last *key* in the database.
def last_key=(x : Int32)
file = File.open(key_file, "w")
file << x.to_s
file.close
x
rescue
raise Exception.new "could not update last-key file"
end
# Take a database key and convert it in a formated string. Example: 343 -> "0000000343"
def stringify_key(key : Int32)
# Negative numbers give strange results with Crystal’s printf.
if key >= 0
"%010i" % key
else
key.to_s
end
end
# Adds a value to the database without a locking mechanism.
#
# For a thread-safe version, use `#<<`.
#
# WARNING: not thread-safe.
def unsafe_add(item : V)
key = last_key + 1
self[key] = item
self.last_key = key
key # FIXME: Should we really return the internal key?
rescue e
raise e
end
# Adds a value to the database, with a locking mechanism to prevent race conditions.
#
# This operation should be thread-safe since a lock is required before tinkering with the database.
# Because of the file-system operations, this function may be a bit slow.
# For single-thread applications, use the `#unsafe_add` operation instead.
def <<(item : V)
request_lock "key"
key = last_key + 1
self[key] = item
self.last_key = key
release_lock "key"
key # FIXME: Should we really return the internal key?
rescue e
release_lock "key"
raise e
end
# Lists all entries in the database.
#
# WARNING: Very slow. Try not to use.
def each(reversed : Bool = false, offset = 0, limit : Int32? = nil)
each_with_key(
reversed: reversed,
offset: offset,
limit: limit
) do |item, key|
yield item
end
end
# Converts all the database into an array.
#
# WARNING: Very slow. Try not to use.
def to_a(reversed : Bool = false, offset = 0, limit : Int32? = nil)
array = ::Array(V).new
each(
reversed: reversed,
offset: offset,
limit: limit
) do |value|
array << value
end
array
end
# Converts the entire database into a hash.
#
# WARNING: Very slow. Try not to use.
def to_h(reversed : Bool = false, offset = 0, limit : Int32? = nil)
hash = ::Hash(Int32, V).new
each_with_key(
reversed: reversed,
offset: offset,
limit: limit
) do |element, key|
hash[key] = element
end
hash
end
# Writes all indexes (basic indexes, partitions, tags, etc.) for a value.
def write_indexes(key : Int32, value : V)
@indexers.each &.index(stringify_key(key), value)
end
# Creates a new basic index **with a cache**.
# The *name* parameter is the name of the directory that will be created.
def new_index(name : String, &block : Proc(V, String | DODB::NoIndex))
CachedIndex(V).new(self, @directory_name, name, block).tap do |indexer|
@indexers << indexer
end
end
# Creates a new basic index **without a cache**.
# The *name* parameter is the name of the directory that will be created.
#
# NOTE: this will be a lot slower than the cached version.
def new_uncached_index(name : String, &block : Proc(V, String | DODB::NoIndex))
Index(V).new(self, @directory_name, name, block).tap do |indexer|
@indexers << indexer
end
end
# Creates a new basic index **only in RAM**.
# The *name* parameter is the name of the directory that will be created.
#
# NOTE: this index is the fastest, but doesn't have a file-system representation.
def new_RAM_index(name : String, &block : Proc(V, String | DODB::NoIndex))
RAMOnlyIndex(V).new(self, @directory_name, name, block).tap do |indexer|
@indexers << indexer
end
end
# Gets an *index object* based on its name.
def get_index(name : String, key)
index = @indexers.find &.name.==(name)
index.not_nil!.as(DODB::Index).get key
end
# Creates a new partition **with a cache**.
# The *name* parameter is the name of the directory that will be created.
def new_partition(name : String, &block : Proc(V, String | DODB::NoIndex))
CachedPartition(V).new(self, @directory_name, name, block).tap do |table|
@indexers << table
end
end
# Creates a new partition **without a cache**.
# The *name* parameter is the name of the directory that will be created.
#
# NOTE: this will be a lot slower than the cached version.
def new_uncached_partition(name : String, &block : Proc(V, String | DODB::NoIndex))
Partition(V).new(self, @directory_name, name, block).tap do |table|
@indexers << table
end
end
# Creates a new partition **only in RAM**.
# The *name* parameter is the name of the directory that will be created.
#
# NOTE: this partition index is the fastest but doesn't have a file-system representation.
def new_RAM_partition(name : String, &block : Proc(V, String | DODB::NoIndex))
RAMOnlyPartition(V).new(self, @directory_name, name, block).tap do |table|
@indexers << table
end
end
# Gets an *index (partition) object* based on its name.
def get_partition(table_name : String, partition_name : String)
partition = @indexers.find &.name.==(table_name)
partition.not_nil!.as(DODB::Partition).get partition_name
end
# Creates a new tag **with a cache**.
# The *name* parameter is the name of the directory that will be created.
def new_tags(name : String, &block : Proc(V, Array(String) | DODB::NoIndex))
CachedTags(V).new(self, @directory_name, name, block).tap do |tags|
@indexers << tags
end
end
# Creates a new tag **without a cache**.
# The *name* parameter is the name of the directory that will be created.
#
# NOTE: this will be a lot slower than the cached version.
def new_uncached_tags(name : String, &block : Proc(V, Array(String) | DODB::NoIndex))
Tags(V).new(self, @directory_name, name, block).tap do |tags|
@indexers << tags
end
end
# Creates a new partition **only in RAM**.
# The *name* parameter is the name of the directory that will be created.
#
# NOTE: this tag index is the fastest but doesn't have a file-system representation.
def new_RAM_tags(name : String, &block : Proc(V, Array(String) | DODB::NoIndex))
RAMOnlyTags(V).new(self, @directory_name, name, block).tap do |tags|
@indexers << tags
end
end
# Gets an *index (tag) object* based on its name.
def get_tags(name, key : String)
tag = @indexers.find &.name.==(name)
tag.not_nil!.as(DODB::Tags).get name, key
end
# WARNING: directed graphs haven't been reviewed in YEARS, assume as dead code.
def new_directed_graph(name : String, index : DODB::Index(V), &block : Proc(V, Array(String))) : DirectedGraph(V)
DirectedGraph(V).new(self, @directory_name, index, name, block).tap do |table|
@indexers << table
end
end
# Checks for collisions in the indexes.
def check_collisions!(key : Int32, value : V, old_value : V?)
@indexers.each &.check!(stringify_key(key), value, old_value)
end
# Retrieves a value and remove it from the database.
def pop
request_lock "key"
key = last_key
# Some entries may have been removed. We’ll skip over those.
# Not the most efficient if a large number of indices are empty.
while key >= 0 && self[key]?.nil?
key = key - 1
end
if key < 0
return nil
end
poped = self[key]
self.unsafe_delete key
last_key = key - 1
release_lock "key"
poped
end
private def data_path
"#{@directory_name}/data"
end
private def file_path(key : Int32)
"#{data_path}/%010i" % key
end
private def locks_directory : String
"#{@directory_name}/locks"
end
private def get_lock_file_path(name : String, subname : String? = nil)
if subname
"#{locks_directory}/#{name}-#{subname}.lock" # FIXME: Separator that causes less collisions?
else
"#{locks_directory}/#{name}.lock"
end
end
private def read(file_path : String)
V.from_json ::File.read file_path
end
private def remove_data!
FileUtils.rm_rf data_path
Dir.mkdir_p data_path
end
private def remove_indexing!
@indexers.each do |indexer|
indexer.nuke_index
end
end
# Removes all indices and then rewrites them all.
#
# WARNING: slow operation.
def reindex_everything!
remove_indexing!
each_with_key() do |item, key|
write_indexes key, item
end
end
# Removes all indexes of a value.
def remove_indexes(key : Int32, value : V)
@indexers.each &.deindex(stringify_key(key), value)
end
# Gets the data with the *key*.
# In case the data is missing, returns *nil*.
def []?(key : Int32) : V?
self[key]
rescue MissingEntry
# FIXME: Only rescue JSON and “no such file” errors.
return nil
end
# Gets the data with the *key*.
# In case the data is missing, returns an exception `DODB::MissingEntry`.
def [](key : Int32) : V
raise MissingEntry.new(key) unless ::File.exists? file_path key
read file_path key
end
# Replaces the data with the *key*.
# In case the data is missing, returns an exception `DODB::MissingEntry`.
def []=(key : Int32, value : V)
old_value = self.[key]?
check_collisions! key, value, old_value
# Removes any old indices or partitions pointing to a value about
# to be replaced.
if old_value
remove_indexes key, old_value
end
# Avoids corruption in case the application crashes while writing.
file_path(key).tap do |path|
::File.write "#{path}.new", value.to_json
::FileUtils.mv "#{path}.new", path
end
write_indexes key, value
if key > last_key
self.last_key = key
end
end
# Deletes the data with the *key* but doesn't request for a lock.
# This function is required since `#pop` is already locked before trying to remove an entry,
# thus calling `#unsafe_delete`.
def unsafe_delete(key : Int32)
value = self[key]?
return if value.nil?
begin
::File.delete file_path key
rescue File::NotFoundError
end
remove_indexes key, value
value
end
# Deletes the data with the *key*.
def delete(key : Int32)
request_lock "key"
value = unsafe_delete key
release_lock "key"
value
end
# Lists all the keys in the database.
private def each_key(reversed = false)
# Removes the first two "." and ".." directories.
keys = Dir.entries(data_path).[2..].map(&.to_i).sort
(reversed ? keys.reverse : keys).each do |key|
yield key
end
end
# Lists all database entries with their key.
# Can be useful for making dumps or to restore a database.
#
# WARNING: Very slow. Try not to use.
def each_with_key(reversed : Bool = false, offset = 0, limit : Int32? = -1)
limit = if l = limit
l
else
-1
end
each_key(reversed) do |key|
offset -= 1 if offset >= 0
next if offset >= 0
return if limit == 0
limit -= 1 if limit > 0
begin
# FIXME: Only intercept JSON parsing errors.
value = self[key]
rescue
next
end
yield value, key
end
end
end

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@ -0,0 +1,6 @@
# Basic database of DODB.
# Data isn't cached.
#
# NOTE: slow but doesn't require much memory.
class DODB::DataBase(V) < DODB::Storage(V)
end