Added power snapshot section to README.md

README.md

@@ -203,3 +203,47 @@ in below image links
 #### Verify social network accounts ( for project verification flow)
 
 [![](https://mermaid.ink/img/pako:eNrFVcFu2zAM_RXCl7VAmgA9-hCga9euQJcNS7tTgEGVaEeNLXkSnSwo-u-jJDtJ03TYgA7zyYbI98j3aOoxk1Zhlmcef7RoJF5oUTpRzwzwIyRZB3ceXfpuhCMtdSMMwaWzhtColyfvhVwcPJhOQHiYWqlFBROklXULCGEzk4J7TDgZj3uYHM5FVYFQaoKrlPvF2UJXCHVLgrQ1cOQ5UJsSfDzvoQUjNc4-oKRv6HShZQy_tK6-VseJ0lhCsEt0W74pEmjTtARKkOBXcKi0j3AlGnSCUwSQ4wQmPWcBX8X6JEIItK6C-zXISqOhazWIiI7ruuODAQyHw4TQ5cFJEKBXI4evDql1JsAcEGo64YgOD1o2C8h2SoDppVDKofcpm32IBMHYHM78YpPlUCiQ1rCeFPutbKk7c0I0bAhvwsFLom5uKoIL7aV13RT0rLu2vih55Hfd9SPJvt9z9EglKFhpmvNMSm7kO1lGCd7w2Lo1eHKs85ZsI-R4HKq9Yktj_doUNjiRUG4DyPMK90pMsveZKXQz26HNK2vLCt-iyzIiDVKX4a_8o-6iGdPwEVOYoORe_6q9neDouVZJ3W3mgcG-wFRiFwtHoOmdh4cVHXc_Smr5OgheOFsDzdHhjoJbDW-0WbBM5i1UrDqs_6bjvnb7HHGbzYkan49GotHDvuKhtPVoeTqq8TdUYdG9Oo8HbLqKu6y3IO2xKMzu9oqG0dzZFeBPiU3cqbpIjjIoLEWlX-c4560RN-IyLllU8MyciO6wCjGagrIHdjIUvJS3E_H57O7242naPuDbKOxhSbdLsuh3YtmuPfi5bSt-10tkvbi4IHNg4UZZg6Z1jfW4J-AefSG4fPWPebNBVqOrhVZ8Cz_G2zDjX4WnIMv5VWEh2opm2cw8cWjb8J2EH5TmiznLC1F5HGSiJTtdG5nl5Frsg7qbvIt6-gW6nqHe)](https://mermaid-js.github.io/mermaid-live-editor/edit#pako:eNrFVcFu2zAM_RXCl7VAmgA9-hCga9euQJcNS7tTgEGVaEeNLXkSnSwo-u-jJDtJ03TYgA7zyYbI98j3aOoxk1Zhlmcef7RoJF5oUTpRzwzwIyRZB3ceXfpuhCMtdSMMwaWzhtColyfvhVwcPJhOQHiYWqlFBROklXULCGEzk4J7TDgZj3uYHM5FVYFQaoKrlPvF2UJXCHVLgrQ1cOQ5UJsSfDzvoQUjNc4-oKRv6HShZQy_tK6-VseJ0lhCsEt0W74pEmjTtARKkOBXcKi0j3AlGnSCUwSQ4wQmPWcBX8X6JEIItK6C-zXISqOhazWIiI7ruuODAQyHw4TQ5cFJEKBXI4evDql1JsAcEGo64YgOD1o2C8h2SoDppVDKofcpm32IBMHYHM78YpPlUCiQ1rCeFPutbKk7c0I0bAhvwsFLom5uKoIL7aV13RT0rLu2vih55Hfd9SPJvt9z9EglKFhpmvNMSm7kO1lGCd7w2Lo1eHKs85ZsI-R4HKq9Yktj_doUNjiRUG4DyPMK90pMsveZKXQz26HNK2vLCt-iyzIiDVKX4a_8o-6iGdPwEVOYoORe_6q9neDouVZJ3W3mgcG-wFRiFwtHoOmdh4cVHXc_Smr5OgheOFsDzdHhjoJbDW-0WbBM5i1UrDqs_6bjvnb7HHGbzYkan49GotHDvuKhtPVoeTqq8TdUYdG9Oo8HbLqKu6y3IO2xKMzu9oqG0dzZFeBPiU3cqbpIjjIoLEWlX-c4560RN-IyLllU8MyciO6wCjGagrIHdjIUvJS3E_H57O7242naPuDbKOxhSbdLsuh3YtmuPfi5bSt-10tkvbi4IHNg4UZZg6Z1jfW4J-AefSG4fPWPebNBVqOrhVZ8Cz_G2zDjX4WnIMv5VWEh2opm2cw8cWjb8J2EH5TmiznLC1F5HGSiJTtdG5nl5Frsg7qbvIt6-gW6nqHe)
+
+
+
+### Power Snapshot
+
+Impact graph supports ranking projects based on power boosted by users. 
+Users who have GIVpower, can boost a project by allocating a portion (percentage) of their GIVpower to that project and after that impact-graph regularly takes snapshot of user GIVpower balance and boost percentages.
+At the end of each givback round (14 days), average of allocated power will be the effective power balance of each project. 
+
+Snapshotting mechanism is implemented in by the hlp of database cron job and impact graph support of historic user balance on blockchain.
+##### Database Snapshot
+Snapshot taking on database is implemented by the help `pg_cron` extension on Postgres database.
+On regular interval (defined by cron job expression), calls a db procedure called public."TAKE_POWER_BOOSTING_SNAPSHOT". 
+This procedure creates a new record of power_snapshot and copies power boosting percentages content to another table and associates them to the new power_snapshot record.
+###### Cron Job Creation
+Cron job creation for test environment is already implemented in dbCronRepository.ts and a modified docker with enabled `pg_cron` extension.
+Giveth uses digitalocean database in production and staging environment and setting snapshot cron job is done manually there because of the digital ocean restriction on configuring `pg_cron` extension.
+Creating snapshot cronjob on digital ocean postgres database step:
+1. Connect to database by `doadmin` user (database owner).
+2. Create cron job by sql command
+```sql
+CREATE EXTENSION IF NOT EXISTS PG_CRON;
+SELECT CRON.schedule(
+    'take givpower boosting snapshot',
+    '*/5 * * * *',
+    $$CALL public."TAKE_POWER_BOOSTING_SNAPSHOT"()$$);
+```
+The cronjob expression above `*/5 * * * *` is for getting snapshot every 5 minutes in the test env. It can be a different schedule based on requirements.
+3. Find created job id by running
+```sql
+SELECT * FROM cron.job
+ORDER BY jobid DESC 
+```
+![img.png](docs/img/pg_cron_jobs.png)
+4. Alter the job (found its id above, supposed here 1) database to whatever is set for impact-graph, here `deveop`. 
+```sql
+select cron.alter_job(job_id:=1,database:='develop');
+```
+
+##### User GIVpower balance snapshot
+impact-graph monitors power_snapshot table and whenever a new record is created it find corresponding ethereum blockchain block number and fills in the snapshot record.
+Then for every user who has a percentage snapshot, fills balance snapshot table with the user balance at the corresponding block number by the help of impact graph block filter.
+
+