Method cacheMmap

core/src/main/java/io/questdb/std/MmapCache.java:91–109

Maps file region into memory, reusing existing mapping if available. @param fd file descriptor to map @param mmapCacheKey unique value that is safe to use as a key for caching the map. FD is not good enough since a FD can be closed after the mapping is created and OS c

(int fd, long mmapCacheKey, long len, long offset, int flags, int memoryTag)

     * @param flags        memory mapping flags, e.g., Files.MAP_RO for read-only
     */
    public long cacheMmap(int fd, long mmapCacheKey, long len, long offset, int flags, int memoryTag) {
        if (len < 1) {
            throw CairoException.critical(0)
                    .put("could not mmap file, invalid len [len=").put(len)
                    .put(", offset=").put(offset)
                    .put(", fd=").put(fd)
                    .put(", memoryTag=").put(memoryTag)
                    .put(']');
        }
        if (offset != 0 || mmapCacheKey == 0 || !Files.FS_CACHE_ENABLED || flags == Files.MAP_RW) {
            return mmap0(fd, len, offset, flags, memoryTag);
        }

        if (Files.ASYNC_MUNMAP_ENABLED) {
            return cacheMmapOptimistic(fd, mmapCacheKey, len, memoryTag);
        } else {
            return cacheMmapPessimistic(fd, mmapCacheKey, len, memoryTag);
        }
    }

    /**
     * Returns number of times cached memory mappings were reused.