Jira Link: DB-1616
design doc: https://github.com/jaki/ysql-gin-doc/releases.

ybgin is to gin as lsm is to btree.

Stage 1 (Release target: v2.11)

1. feat: add system catalog entries for new opclass ybgin
2. refactor: transparently change USING gin to use ybgin on Yugabyte tables (ysql: transparently change gin to ybgin #8402)
3. feat: implement limited functionality for ybgin
4. refactor: turn PrepareIndexWriteStmt to callback ([YSQL] Turn PrepareIndexWriteStmt to callback #10406)
5. feat: support text search (YSQL - full text search  #3446)
   • feat: support text search configurations ([YSQL] text search configuration "english" does not exist #1979)
   • feat: support prefix match for tsvector ([YSQL] Support GIN indexes for tsvector values #9955)
   • feat: support gin on extension pg_trgm (ysql: support gin index in pg_trgm extension #9595)
6. feat: support writing null categories (ysql: support writing ybgin null categories #9959)
7. feat: redirect unsupported scans to sequential scan (cost estimates) (ysql: use sequential scan instead of unsupported ybgin scan #9960)

Stage 2

• feat: support multicolumn ([YSQL] Support multicolumn GIN indexes #10652)
• feat: support gin on remaining extensions
  • feat: support gin on extension btree_gin (ysql: support btree_gin extension #9958)
  • feat: support gin on extension hstore (ysql: support gin index in hstore extension #9956)
• feat: support all scans
  • feat: support multiple required scan entries
  • feat: support multiple scan keys
  • feat: support non-default search modes
• feat: do type-specific changes, if any
  • jsonb ([YSQL] Support GIN indexes on jsonb values #7851)
  • anyarray ([YSQL] Support GIN indexes for array values #7852)
• perf: improve cost estimates
• feat: support ASC/DESC/HASH ([YSQL] Support ASC/DESC/HASH on GIN indexes #10653)

Future

• perf: do smarter scans using parallel scan streams
• perf: don't always recheck tuples
• feat: support IndexOnlyScan (this is not in upstream PostgreSQL)