Add a readme for import validator

cmd/import-validator/README.md

@@ -0,0 +1,49 @@
+# Import validation tool
+
+The import validator tool imports blocks into indexer database and algod's
+sqlite database in lockstep and checks that the modified accounts are the same
+in the two databases.
+It lets us detect the first round where an accounting discrepancy occurs
+and it prints out the difference before crashing.
+
+There is a small limitation, however.
+The set of modified accounts is computed using the sqlite database.
+Thus, if indexer's accounting were to modify a superset of those accounts,
+this tool would not detect it.
+This, however, should be unlikely.
+
+# Using the tool
+
+Running the tool is similar to running `algorand-indexer` with the exception
+that one has to specify the path to the sqlite (go-algorand) database.
+
+Create a new postgres (indexer) database.
+```
+createdb db0
+```
+
+Create a directory for the sqlite (go-algorand) database.
+This will essentially serve as a non-archival algod database.
+```
+mkdir ledger
+```
+
+Run the tool.
+```
+./import-validator --algod-net localhost:8080 --algod-token ALGOD_TOKEN --algod-ledger ledger --postgres "user=ubuntu host=localhost database=db0 sslmode=disable"
+```
+
+The tool can be safely stopped and started again.
+Also, the provided indexer database can be created by indexer itself, and the
+provided ledger sqlite database can be created by algod.
+Since the import validator essentially exercises indexer's and go-algorand's
+database code, this should work.
+However, the sqlite database must be at the same round as the postgres database
+or one round behind; otherwise, the import validator will fail to start.
+
+# Performance
+
+Reading and writing to/from the sqlite database is negligible compared to
+importing blocks into the postgres database.
+However, the tool has to read the modified accounts after importing each block.
+Thus, we can expect the import validator to be 1.5 times slower than indexer.

cmd/import-validator/main.go

@@ -1,11 +1,3 @@
-// The import validator tool imports blocks into indexer database and algod's sqlite
-// database in lockstep and checks that the modified accounts are the same in the two
-// databases. It lets detect the first round where an accounting discrepancy occurs
-// and it prints out what the difference is before crashing.
-// There is a small limitation, however. The set of modified accounts is computed using
-// the sqlite database. Thus, if indexer's accounting were to modify a superset of
-// those accounts, this tool would not detect it. This, however, should be unlikely.
-
 package main
 
 import (