1 Commits

Author	SHA1	Message	Date
guybe7	03fcc211de	A better approach for COMMAND INFO for movablekeys commands (#8324) ... Fix #7297 The problem: Today, there is no way for a client library or app to know the key name indexes for commands such as ZUNIONSTORE/EVAL and others with "numkeys", since COMMAND INFO returns no useful info for them. For cluster-aware redis clients, this requires to 'patch' the client library code specifically for each of these commands or to resolve each execution of these commands with COMMAND GETKEYS. The solution: Introducing key specs other than the legacy "range" (first,last,step) The 8th element of the command info array, if exists, holds an array of key specs. The array may be empty, which indicates the command doesn't take any key arguments or may contain one or more key-specs, each one may leads to the discovery of 0 or more key arguments. A client library that doesn't support this key-spec feature will keep using the first,last,step and movablekeys flag which will obviously remain unchanged. A client that supports this key-specs feature needs only to look at the key-specs array. If it finds an unrecognized spec, it must resort to using COMMAND GETKEYS if it wishes to get all key name arguments, but if all it needs is one key in order to know which cluster node to use, then maybe another spec (if the command has several) can supply that, and there's no need to use GETKEYS. Each spec is an array of arguments, first one is the spec name, the second is an array of flags, and the third is an array containing details about the spec (specific meaning for each spec type) The initial flags we support are "read" and "write" indicating if the keys that this key-spec finds are used for read or for write. clients should ignore any unfamiliar flags. In order to easily find the positions of keys in a given array of args we introduce keys specs. There are two logical steps of key specs: 1. `start_search`: Given an array of args, indicate where we should start searching for keys 2. `find_keys`: Given the output of start_search and an array of args, indicate all possible indices of keys. ### start_search step specs - `index`: specify an argument index explicitly - `index`: 0 based index (1 means the first command argument) - `keyword`: specify a string to match in `argv`. We should start searching for keys just after the keyword appears. - `keyword`: the string to search for - `start_search`: an index from which to start the keyword search (can be negative, which means to search from the end) Examples: - `SET` has start_search of type `index` with value `1` - `XREAD` has start_search of type `keyword` with value `[“STREAMS”,1]` - `MIGRATE` has start_search of type `keyword` with value `[“KEYS”,-2]` ### find_keys step specs - `range`: specify `[count, step, limit]`. - `lastkey`: index of the last key. relative to the index returned from begin_search. -1 indicating till the last argument, -2 one before the last - `step`: how many args should we skip after finding a key, in order to find the next one - `limit`: if count is -1, we use limit to stop the search by a factor. 0 and 1 mean no limit. 2 means ½ of the remaining args, 3 means ⅓, and so on. - “keynum”: specify `[keynum_index, first_key_index, step]`. - `keynum_index`: is relative to the return of the `start_search` spec. - `first_key_index`: is relative to `keynum_index`. - `step`: how many args should we skip after finding a key, in order to find the next one Examples: - `SET` has `range` of `[0,1,0]` - `MSET` has `range` of `[-1,2,0]` - `XREAD` has `range` of `[-1,1,2]` - `ZUNION` has `start_search` of type `index` with value `1` and `find_keys` of type `keynum` with value `[0,1,1]` - `AI.DAGRUN` has `start_search` of type `keyword` with value `[“LOAD“,1]` and `find_keys` of type `keynum` with value `[0,1,1]` (see https://oss.redislabs.com/redisai/master/commands/#aidagrun) Note: this solution is not perfect as the module writers can come up with anything, but at least we will be able to find the key args of the vast majority of commands. If one of the above specs can’t describe the key positions, the module writer can always fall back to the `getkeys-api` option. Some keys cannot be found easily (`KEYS` in `MIGRATE`: Imagine the argument for `AUTH` is the string “KEYS” - we will start searching in the wrong index). The guarantee is that the specs may be incomplete (`incomplete` will be specified in the spec to denote that) but we never report false information (assuming the command syntax is correct). For `MIGRATE` we start searching from the end - `startfrom=-1` - and if one of the keys is actually called "keys" we will report only a subset of all keys - hence the `incomplete` flag. Some `incomplete` specs can be completely empty (i.e. UNKNOWN begin_search) which should tell the client that COMMAND GETKEYS (or any other way to get the keys) must be used (Example: For `SORT` there is no way to describe the STORE keyword spec, as the word "store" can appear anywhere in the command). We will expose these key specs in the `COMMAND` command so that clients can learn, on startup, where the keys are for all commands instead of holding hardcoded tables or use `COMMAND GETKEYS` in runtime. Comments: 1. Redis doesn't internally use the new specs, they are only used for COMMAND output. 2. In order to support the current COMMAND INFO format (reply array indices 4, 5, 6) we created a synthetic range, called legacy_range, that, if possible, is built according to the new specs. 3. Redis currently uses only getkeys_proc or the legacy_range to get the keys indices (in COMMAND GETKEYS for example). "incomplete" specs: the command we have issues with are MIGRATE, STRALGO, and SORT for MIGRATE, because the token KEYS, if exists, must be the last token, we can search in reverse. it one of the keys is actually the string "keys" will return just a subset of the keys (hence, it's "incomplete") for SORT and STRALGO we can use this heuristic (the keys can be anywhere in the command) and therefore we added a key spec that is both "incomplete" and of "unknown type" if a client encounters an "incomplete" spec it means that it must find a different way (either COMMAND GETKEYS or have its own parser) to retrieve the keys. please note that all commands, apart from the three mentioned above, have "complete" key specs	2021-09-15 11:10:29 +03:00