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Memory is only needed if it is read in the future, but short of having a time machine, how can an implementation tell what code the program will execute and which data it will use? Latency is the longest continuous chunk of time where the user’s program is completely paused while garbage collection happens. In comparison, TTL gates typically had a difference of about 3.2 volts between a "0" and a "1", requiring more time to switch. However, it is commonly known that MyISAM is more vulnerable to data corruption than most serious database applications would tolerate, and after a crash it can take a long time to repair the tables, during which the server is down. However, these APIs are seldom used and even when they are used it is difficult to imagine a scenario where the change might break something. There is a precedent for this with Perl and Python etc. Dave, Magnus, and David Wheeler were talking about the PGXN site, Pool Table Size and the Perl modules are a PITA.

Ran into this for AIO for WAL insert and every AIO for WAL insert had to be reserved and is in critical section and you can't allocate memory there. In memory, modify the data pages in shared buffers, and then write the change into the WAL buffer. Then cleans up some collections. Bit-slice processors such as the Am2901 were used in minicomputers and many other systems in the 1970s and 1980s. Eventually, though, improvements in CMOS technology permitted a fast processor to be implemented on a single chip, rendering the bit-slice processor obsolete. 3. A popular alternative to the Am2901 in many minicomputers was the 74181 ALU chip. 1. Microprocessors on a single chip existed at the time, but they used MOS transistors that were slower than the bipolar transistors used in most minicomputers. If B and C are both low, current through the Vref transistors pulls the output low.

This is an improvement over a simple resistor, since the current through the resistor varies based on the voltage across it, which depends on the input voltages. Once the two ALU inputs have been selected, the ALU computes "Propagate" (P) and "Generate" (G) bits for each pair of input bits. Addition is performed by bitwise EXCLUSIVE OR of the two arguments and the carry bits. The ALU performs one of eight functions on its two 4-bit inputs: R and S. At the right are various outputs from the chip: G, P, carry out, sign, overflow, and zero test. The chip's ALU is spread across the lower half of the chip, implementing eight different functions and using carry lookahead for high performance. C (where C is the carry-in), there's no way to get a carry out from that addition, regardless of what C is. Each chip generates a Generate and Propagate signal, indicating if that chip will generate a carry or propagate a carry-in.

The P and G signals from the previous circuit go to two blocks of carry computation circuitry. The multiplexers above the ALU in the block diagram are physically part of the ALU circuitry on the die. Putting this all together, for each bit position you create a G (generate) signal if both bits are 1, and a P (propagate) signal unless both bits are 0, using simple logic gates. 14. The carry lookahead techniques can be implemented across multiple chips for fast additions larger than 4 bits. Three of the instruction bits fed into the chip are used to select the operation: I5, I4, and I3. SLRUs are pretty small so that is ok. On the other hand, the small voltage swings of ECL made the circuits more sensitive to electrical noise. Schematic of an ECL AND-XOR circuit. The key point is that a single ECL gate can implement a complex function; in contrast, XOR is difficult with most logic families. 15. The output circuitry also includes multiplexers; the chip can either output the ALU result or the A register value. The "sum" circuitry computes the sum for each bit using the carry, P, and G values. The lower carry block computes external P, G, and carry signals that provide carry lookahead across multiple chips; this allows fast addition for larger words.14 The upper carry block computes the carries that are used internally.