# SPDX-License-Identifier: Apache-2.0 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project """ Demonstration script for Automatic Prefix Caching (APC) in vLLM. Automatic Prefix Caching (APC) allows the vLLM engine to reuse cached KV (key-value) pairs from previous prompts if a new query shares the same prefix. This reduces redundant computation and improves inference speed. To enable APC, set `enable_prefix_caching=True` when initializing the vLLM engine. This script uses a long Markdown table as the shared prompt prefix and compares the generation time for two queries that share the same prefix but ask different questions. Run: python examples/offline_inference/automatic_prefix_caching.py """ import time from vllm import LLM, SamplingParams # ruff: noqa: E501 # A prompt containing a large markdown table. The table is randomly generated by GPT-4. LONG_PROMPT = ( "You are a helpful assistant in recognizes the content of tables in markdown format. Here is a table as follows.\n# Table\n" + """ | ID | Name | Age | Occupation | Country | Email | Phone Number | Address | |-----|---------------|-----|---------------|---------------|------------------------|----------------|------------------------------| | 1 | John Doe | 29 | Engineer | USA | john.doe@example.com | 555-1234 | 123 Elm St, Springfield, IL | | 2 | Jane Smith | 34 | Doctor | Canada | jane.smith@example.com | 555-5678 | 456 Oak St, Toronto, ON | | 3 | Alice Johnson | 27 | Teacher | UK | alice.j@example.com | 555-8765 | 789 Pine St, London, UK | | 4 | Bob Brown | 45 | Artist | Australia | bob.b@example.com | 555-4321 | 321 Maple St, Sydney, NSW | | 5 | Carol White | 31 | Scientist | New Zealand | carol.w@example.com | 555-6789 | 654 Birch St, Wellington, NZ | | 6 | Dave Green | 28 | Lawyer | Ireland | dave.g@example.com | 555-3456 | 987 Cedar St, Dublin, IE | | 7 | Emma Black | 40 | Musician | USA | emma.b@example.com | 555-1111 | 246 Ash St, New York, NY | | 8 | Frank Blue | 37 | Chef | Canada | frank.b@example.com | 555-2222 | 135 Spruce St, Vancouver, BC | | 9 | Grace Yellow | 50 | Engineer | UK | grace.y@example.com | 555-3333 | 864 Fir St, Manchester, UK | | 10 | Henry Violet | 32 | Artist | Australia | henry.v@example.com | 555-4444 | 753 Willow St, Melbourne, VIC| | 11 | Irene Orange | 26 | Scientist | New Zealand | irene.o@example.com | 555-5555 | 912 Poplar St, Auckland, NZ | | 12 | Jack Indigo | 38 | Teacher | Ireland | jack.i@example.com | 555-6666 | 159 Elm St, Cork, IE | | 13 | Karen Red | 41 | Lawyer | USA | karen.r@example.com | 555-7777 | 357 Cedar St, Boston, MA | | 14 | Leo Brown | 30 | Chef | Canada | leo.b@example.com | 555-8888 | 246 Oak St, Calgary, AB | | 15 | Mia Green | 33 | Musician | UK | mia.g@example.com | 555-9999 | 975 Pine St, Edinburgh, UK | | 16 | Noah Yellow | 29 | Doctor | Australia | noah.y@example.com | 555-0000 | 864 Birch St, Brisbane, QLD | | 17 | Olivia Blue | 35 | Engineer | New Zealand | olivia.b@example.com | 555-1212 | 753 Maple St, Hamilton, NZ | | 18 | Peter Black | 42 | Artist | Ireland | peter.b@example.com | 555-3434 | 912 Fir St, Limerick, IE | | 19 | Quinn White | 28 | Scientist | USA | quinn.w@example.com | 555-5656 | 159 Willow St, Seattle, WA | | 20 | Rachel Red | 31 | Teacher | Canada | rachel.r@example.com | 555-7878 | 357 Poplar St, Ottawa, ON | | 21 | Steve Green | 44 | Lawyer | UK | steve.g@example.com | 555-9090 | 753 Elm St, Birmingham, UK | | 22 | Tina Blue | 36 | Musician | Australia | tina.b@example.com | 555-1213 | 864 Cedar St, Perth, WA | | 23 | Umar Black | 39 | Chef | New Zealand | umar.b@example.com | 555-3435 | 975 Spruce St, Christchurch, NZ| | 24 | Victor Yellow | 43 | Engineer | Ireland | victor.y@example.com | 555-5657 | 246 Willow St, Galway, IE | | 25 | Wendy Orange | 27 | Artist | USA | wendy.o@example.com | 555-7879 | 135 Elm St, Denver, CO | | 26 | Xavier Green | 34 | Scientist | Canada | xavier.g@example.com | 555-9091 | 357 Oak St, Montreal, QC | | 27 | Yara Red | 41 | Teacher | UK | yara.r@example.com | 555-1214 | 975 Pine St, Leeds, UK | | 28 | Zack Blue | 30 | Lawyer | Australia | zack.b@example.com | 555-3436 | 135 Birch St, Adelaide, SA | | 29 | Amy White | 33 | Musician | New Zealand | amy.w@example.com | 555-5658 | 159 Maple St, Wellington, NZ | | 30 | Ben Black | 38 | Chef | Ireland | ben.b@example.com | 555-7870 | 246 Fir St, Waterford, IE | """ ) def get_generation_time(llm, sampling_params, prompts): # time the generation start_time = time.time() output = llm.generate(prompts, sampling_params=sampling_params) end_time = time.time() # print the output and generation time print("-" * 30) print(f"Output: {output[0].outputs[0].text}") print(f"Generation time: {end_time - start_time} seconds.") print("-" * 30) def main(): # set enable_prefix_caching=True to enable APC llm = LLM(model="lmsys/longchat-13b-16k", enable_prefix_caching=True) sampling_params = SamplingParams(temperature=0, max_tokens=100) # Querying the age of John Doe get_generation_time( llm, sampling_params, LONG_PROMPT + "Question: what is the age of John Doe? Your answer: The age of John Doe is ", ) # Querying the age of Zack Blue # This query will be faster since vllm avoids computing the KV cache of LONG_PROMPT again. get_generation_time( llm, sampling_params, LONG_PROMPT + "Question: what is the age of Zack Blue? Your answer: The age of Zack Blue is ", ) if __name__ == "__main__": main()