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Inside An AI Agent: Planning, Tool Use, Memory, Constraints, And Verification

Have you noticed how every demo of "an AI agent" looks impressive in the video and falls apart the moment you ask a sharper question? The agent confidently does the wrong thing. It forgets what it just decided. It tries to call a tool that doesn't exist. It loops forever rewriting the same file. It calmly tells you the deployment succeeded when it didn't. These aren't failures of the model. They're failures of the workflow around the model. Because that's all an agent really is: a software workflow where a language model can pick the next step and call tools. The "intelligence" sits in the prompt and the orchestration around it, not in some secret agent-flavoured fairy dust. Strip the word "agent" away and you've got five pieces of plumbing: planning, tool use, memory, constraints, verification. Every production-grade agent stands or falls on those five. This is a long walk through each one. Not the marketing version. The kind of detail you actually need before you ship something that talks to your database. The Loop You're Actually Building Before we touch any pillar individually, hold the whole loop in your head. A useful agent does roughly this on every turn: Read the goal (and whatever memory is relevant to it). Decide the next action: answer directly, call a tool, ask a clarifying question, or stop. If it called a tool, observe the tool's result and feed it back in. Update memory if anything is worth remembering. Check constraints: are we over budget, out of iterations, touching something off-limits? Verify the output before declaring success. Loop until done or stopped. That's it. Every framework (LangGraph, OpenAI Agents SDK, Claude Agent SDK, smolagents, whatever ships next month) is a different shape of the same loop with different defaults. agent-loop.ts async function runAgent ( goal : string , ctx : AgentContext ) { const state = ctx . startState ( goal ); for ( let step = 0 ; step < ctx . maxSteps ; step ++ ) { const decision = await ctx . model . decid

2026-06-28 原文 →
AI 资讯

1.4.10 Planner Hook: When It Fires, How to Use It

Everything from 1.4.1 through 1.4.9 happened inside a single function, standard_planner() . Building paths, costing them, searching for a join order, estimating cardinality from statistics: all of it runs inside that one function. Yet PostgreSQL does not call standard_planner() directly. It puts another function, planner() , one step ahead of it, and has planner() call standard_planner() . And planner() can be made to call some other function instead of standard_planner() . That replacement is what the planner hook enables. When pg_stat_statements measures per-query planning time, or pg_hint_plan rewrites a plan according to hints, it all goes through this hook. Let's look at how PostgreSQL provides a way to observe or change planning behavior without touching a single line of the core, and how external code plugs into it. All planner() does is check the hook The body of planner() is essentially this. if ( planner_hook ) result = ( * planner_hook ) ( parse , query_string , cursorOptions , boundParams ); else result = standard_planner ( parse , query_string , cursorOptions , boundParams ); planner_hook is a global function pointer. Its default value is NULL , in which case standard_planner() is called right away. A plain PostgreSQL build always takes this path: planner_hook is empty, so the incoming query goes straight to standard_planner() . The key here is the type of planner_hook . typedef PlannedStmt * ( * planner_hook_type ) ( Query * parse , const char * query_string , int cursorOptions , ParamListInfo boundParams ); This signature is identical, down to the character, to that of planner() and standard_planner() . It takes the same Query and returns the same PlannedStmt (the execution plan). So external code only has to write a planner function matching this type and store its address in planner_hook . Let's call this function, written by external code to register in planner_hook , a custom planner function. The moment its address is stored, every planning reque

2026-06-21 原文 →