Plug the new PG combinator into monitor

2024-04-07 02:44:17 +03:00
parent 29284bef40
commit 3629dbc54d
13 changed files with 362 additions and 23 deletions
@@ -32,6 +32,8 @@ Parameters:
 - [pg_minsize](#pg_minsize)
 - [pg_count](#pg_count)
 - [failure_domain](#failure_domain)
+- [level_placement](#level_placement)
+- [raw_placement](#raw_placement)
 - [max_osd_combinations](#max_osd_combinations)
 - [block_size](#block_size)
 - [bitmap_granularity](#bitmap_granularity)
@@ -209,6 +211,69 @@ never put on OSDs in the same failure domain (for example, on the same host).
 So failure domain specifies the unit which failure you are protecting yourself
 from.

+## level_placement
+
+- Type: string
+
+Additional failure domain rules, applied in conjuction with failure_domain.
+Must be specified in the following form:
+
+`<placement level>=<sequence of characters>, <level2>=<sequence2>, ...`
+
+Sequence should be exactly [pg_size](#pg_size) character long. Each character
+corresponds to an OSD in the PG of this pool. Equal characters mean that
+corresponding items of the PG should be placed into the same placement tree
+item at this level. Different characters mean that items should be placed into
+different items.
+
+For example, if you want a EC 4+2 pool and you want every 2 chunks to be stored
+in its own datacenter and you also want each chunk to be stored on a different
+host, you should set `level_placement` to `dc=112233 host=123456`.
+
+Or you can set `level_placement` to `dc=112233` and leave `failure_domain` empty,
+because `host` is the default `failure_domain` and it will be applied anyway.
+
+Without this rule, it may happen that 3 chunks will be stored on OSDs in the
+same datacenter, and the data will become inaccessibly if that datacenter goes
+down in this case.
+
+Of course, you should group your hosts into datacenters before applying the rule
+by setting [placement_levels](monitor.en.md#placement_levels) to something like
+`{"dc":90,"host":100,"osd":110}` and add DCs to [node_placement](#placement-tree),
+like `{"dc1":{"level":"dc"},"host1":{"parent":"dc1"},...}`.
+
+## raw_placement
+
+- Type: string
+
+Raw PG placement rules, specified in the form of a DSL (domain-specific language).
+Use only if you really know what you're doing :)
+
+DSL specification:
+
+```
+dsl := item | item ("\n" | ",") items
+item := "any" | rules
+rules := rule | rule rules
+rule := level operator arg
+level := /\w+/
+operator := "!=" | "=" | ">" | "?="
+arg := value | "(" values ")"
+values := value | value "," values
+value := item_ref | constant_id
+item_ref := /\d+/
+constant_id := /"([^"]+)"/
+```
+
+"?=" operator means "preferred". I.e. `dc ?= "meow"` means "prefer datacenter meow
+for this chunk, but put into another dc if it's unavailable".
+
+Examples:
+
+- Simple 3 replicas with failure_domain=host: `any, host!=1, host!=(1,2)`
+- EC 4+2 in 3 DC: `any, dc=1 host!=1, dc!=1, dc=3 host!=3, dc!=(1,3), dc=5 host!=5`
+- 1 replica in fixed DC + 2 in random DCs: `dc?=meow, dc!=1, dc!=(1,2)`
+
 ## max_osd_combinations

 - Type: integer