FPM (FastCGI Process Manager) is an alternative PHP FastCGI implementation
with some additional features (mostly) useful for heavy-loaded sites.
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advanced process management with graceful stop/start;
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ability to start workers with different uid/gid/chroot/environment,
listening on different ports and using different php.ini (replaces safe_mode);
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stdout and stderr logging;
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emergency restart in case of accidental opcode cache destruction;
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accelerated upload support;
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"slowlog" - logging scripts (not just their names, but their PHP backtraces too,
using ptrace and similar things to read remote process' execute_data) that are executed unusually slow;
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fastcgi_finish_request() - special function to finish request and flush all data while
continuing to do something time-consuming (video converting, stats processing etc.);
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dynamic/static child spawning;
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basic SAPI status info (similar to Apache mod_status);
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php.ini-based config file.