Limit warmup memory usage #5524
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fulmicoton
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Related: #5312 |
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Due to tantivy limitations, searching a split requires downloading all of the required data, and keep them in memory. We call this phase warmup. Before this PR, the only thing that curbed memory usage was the search permits: only N split search may happen concurrently. Unfortunately, the amount of data required here varies vastly. We need a mechanism to measure and avoid running more split search when memory is tight. Just using a semaphore is however not an option. We do not know beforehands how much memory will be required by a split search, so it could easily lead to a dead lock. Instead, this commit builds upon the search permit provider. The search permit provider is in charge of managing a configurable memory budget for this warmup memory. We introduce here a configurable "warmup_single_split_initial_allocation". A new leaf split search cannot be started if this memory is not available. This initial allocation is meant to be greater than what will be actually needed most of the time. The split search then holds this allocation until the end of warmup. After warmup, we can get the actual memory usage by interrogating the warmup cache. We can then update the amount of memory held. (most of the time, this should mean releasing some memory) In addition, in this PR, at this point, we also release the warmup search permit: We still have to perform the actual task of searching, but the thread pool will take care of limiting the number of concurrent task. Closes #5355
Also attach the permit to the actual memory cache to ensure memory is freed at the right moment.
Adding an extra generic field into the cache to optionally allow permit tracking is weird. Instead, we make the directory generic on the type of cache and use a wrapped cache when tracking is necessary.
rdettai
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quickwit/quickwit-search/src/root.rs
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| if is_top_1pct_memory_intensive( | ||
| resource_stats.short_lived_cache_num_bytes, | ||
| resource_stats.split_num_docs, | ||
| ) { | ||
| // We log at most 5 times per minute. | ||
| quickwit_common::rate_limited_info!(limit_per_min=5, split_num_docs=resource_stats.split_num_docs, %search_request.query_ast, short_lived_cached_num_bytes=resource_stats.short_lived_cache_num_bytes, query=%search_request.query_ast, "memory intensive query"); | ||
| } |
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should we create a metric as well?
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We also measure the amount of memory taken by a split search, and log this.