Search for online accounts

[agodnic]

Summary

(This pull request is part of the features described in AlgoNode#4. The aforementioned features will be presented in separate, smaller pull requests to make it easier to accept/reject/discuss each one individually)

This pull request adds the online-only parameter to GET /v2/accounts, which lets the user search for accounts whose participation status is "online".

Test Plan

Tested manually in a local environment, e.g.:

$ curl -Ss 'http://127.0.0.1:8980/v2/accounts?limit=10&online-only=true&exclude=all' | jq '.accounts[] .status'
"Online"
"Online"
"Online"
"Online"
"Online"
"Online"
"Online"
"Online"
"Online"
"Online"

Performance

The performance of is-online=true lookups can be improved with the following index:

-- create the index
ledgerdb=# CREATE INDEX account_idx_online_only
        ON account ((((account_data ->> 'onl')) = '1'), addr)
        WHERE (NOT deleted) AND ((account_data ->> 'onl') IS NOT NULL)
;
CREATE INDEX

-- Verify the index is being used by the query optimizer.
-- This query corresponds to /v2/accounts?limit=10&online-only=true&exclude=all
ledgerdb=# explain (analyze) WITH qaccounts AS (SELECT a.addr, a.microalgos, a.rewards_total, a.created_at, a.closed_at, a.deleted, a.rewardsbase, a.keytype, a.account_data FROM account a WHERE NOT a.deleted AND a.account_data->>'onl' IS NOT NULL and (a.account_data->>'onl') = '1' ORDER BY a.addr ASC LIMIT 10) SELECT za.addr, za.microalgos, za.rewards_total, za.created_at, za.closed_at, za.deleted, za.rewardsbase, za.keytype, za.account_data FROM qaccounts za ORDER BY za.addr ASC;
                                                                      QUERY PLAN                                                                      
------------------------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.29..37.65 rows=10 width=103) (actual time=0.013..0.041 rows=10 loops=1)
   ->  Index Scan using account_idx_online_only on account a  (cost=0.29..409750.14 rows=109675 width=103) (actual time=0.012..0.040 rows=10 loops=1)
         Index Cond: (((account_data ->> 'onl'::text) = '1'::text) = true)
 Planning Time: 0.580 ms
 Execution Time: 0.054 ms
(5 rows)

[agodnic]

Discussion

1. If we want to treat suspended accounts differently from other online accounts, my understanding is that we'd need to somehow persist that information in the database (probably within the account table).
   It could be a new integer nullable field: account.account_data->suspended_until

2. A follow-up question would be whether we want to add a parameter in GET /v2/accounts to search for suspended accounts.

[jannotti]

A suspended account has status = 0 (offline) but has non-zero key material (SelectionID, VoterID, etc).