Igniters,
We had several discussion about cache groups [1]. Our current consensus is
that this is not that good design decision - bad scan performance, no API.
A kind of shortcut to solve memory consumption problems. For this reason we
try to avoid exposing "cache group" to API when possible. Also we
understand that current file-per-partition approach is not ideal either -
when there are too many partitions we have to fsync a lot of files. And as
an idea for "bright future" we consider tablespaces - one or several files
where all database objects are stored in dedicated "segments", which are
allocated in smaller units called "extents".
I was thinking on how to "legalize" cache groups on API on the one hand
(product needs them currently), and to let real tablespaces to appear in
future. Idea is simple - treat cache group as special kind of tablespace.
We may say that current storage organization is one type of tablespace, and
proposed "file-segment-extent" storage organization is another type of
tablespace.
With this in mind we can configure tablespaces in IgniteConfiguration, then
assign each cache a tablespace. As advanced tasks we may allow dynamic
table space create/alter/drop, I'll show SQL examples below.
// Interface
interface Tablespace {
String name();
}
// Current non-shared tablespace (aka "physical cache")
class FilePerPartitionTablespace implements Tablespace {
// ...
}
// Shared tablespace (aka "cache group") - note that now we have a legal
place for cache group configuration:
class FilePerPartitionSharedTablespace implements Tablespace {
CacheMode cacheMode;
CacheAtomicityMode cacheAtomicityMode;
AffinityFunction affinityFunction;
// + Other parameters from
ClusterCachesInfo.validateCacheGroupConfiguration
// + Some parameters from "DataRegionConfiguration" (e.g. paths)
}
// Future "real" tablespace
class SegmentedTablespace implements Tablespace {
// Whatever is needed.
}
// Cache configuration
class CacheConfiguration {
...
String tablespace;
...
}
// Managing tablespaces from SQL:
CREATE TABLESPACE my_tbs ENGINE=FILE_PER_PARTITION_SHARED
CACHE_MODE=PARTITIONED BACKUPS=1
ALTER TABLESPACE my_tbs ENCRYPTED=1
CREATE TABLE my_table (...) TABLESPACE my_tbs
What do you think?
Vladimir.
[1]
http://apache-ignite-developers.2346864.n4.nabble.com/Remove-cache-groups-in-AI-3-0-td29184.html
