Re: Proposal: Recent mutated table tracking in memory

Thank you Tatsuo!

Nadav Shatz
Tailor Brands | CTO

On Wed, Jan 28, 2026 at 7:08 AM Tatsuo Ishii <ishii(at)postgresql(dot)org> wrote:

> Hi Nadav,
>
> Sorry for the late reply. I just your email now. Will check and reply
> back soon.
> --
> Tatsuo Ishii
> SRA OSS K.K.
> English: http://www.sraoss.co.jp/index_en/
> Japanese:http://www.sraoss.co.jp
>
> > Hi all,
> >
> > Any comments or concerns? can we merge it if not?
> >
> > On Tue, Jan 6, 2026 at 1:25 PM Nadav Shatz <nadav(at)tailorbrands(dot)com>
> wrote:
> >
> >> Hello,
> >>
> >> As initially proposed under "Proposal: recent access based routing for
> >> primary-replica setups" and then broken into separate tasks - i am
> adding
> >> here a patch to implement tracking of latest mutated table, and then
> using
> >> the replication lag as a base - deciding where to point queries when
> query
> >> load balancing and parsing is enabled.
> >>
> >> More details as in the patch:
> >> Feature: add in-memory table tracking to prevent stale reads from
> replicas
> >>
> >> Implement "memory map" feature that tracks recently-written database
> >> tables in shared memory to prevent stale reads during replication lag.
> >> When a write (INSERT/UPDATE/DELETE) occurs on a table, that table is
> >> marked as "dirty" for a configurable TTL period. Any SELECT on a dirty
> >> table within the TTL window is routed to primary instead of replica.
> >>
> >> Key features:
> >> - Shared memory hash table for tracking table mutations with TTL
> >> - Query parse cache with LRU eviction for performance
> >> - Cold start protection (routes all queries to primary initially)
> >> - Automatic TTL calculation: replication_delay × configurable factor
> >> - Per-table staleness tracking with microsecond precision
> >>
> >> New configuration parameters:
> >> - memory_map_enabled: Enable/disable the feature (default: off)
> >> - memory_map_ttl_factor: TTL multiplier for replication delay (default:
> >> 5.0)
> >> - memory_map_cold_start_duration: Cold start period in ms (default:
> 2000)
> >> - memory_map_table_buckets: Hash buckets for table map (default: 1024)
> >> - memory_map_table_size: Max tracked tables (default: 2048)
> >> - memory_map_query_buckets: Hash buckets for query cache (default: 2048)
> >> - memory_map_query_cache_size: Max cached queries (default: 10000)
> >>
> >> Patch applies properly and tests pass.
> >>
> >> Open to all feedback - thank you!
> >>
> >> --
> >> Nadav Shatz
> >> Tailor Brands | CTO
> >>
> >
> >
> > --
> > Nadav Shatz
> > Tailor Brands | CTO
>