I would say that some part of the Russian experience comes from the Soviet campaign in the aid of the Democratic Republic of Afghanistan. You captured the major Afghan ring road and more or less all the major cities, but then what? The reactionary mujahideen simply retreated to the countryside in the same way the Taliban did following the later American invasion. Funded by American weapons in the same way that NATO now funds Ukraine, the entire strategic paradigm shifts towards an endless defensive slog against counter-insurgency. You can't abandon your own established holdings, the major cities and its peoples, to consolidate properly for both PR/morale and humanitarian reasons and so the conflict is a long bleed. Once an equilibrium is established, you cannot strike out against the mujahideen-occupied countryside without drawing resources used to defend your established urban holdings. The Soviet and US Afghan Wars are examples of how precisely a long war should not be conducted.

The only long war in contemporary history which brutal attrition was the intention is a war that most ML don't study because it's a miserable inter-fraternal conflict between socialist states, the Sino-Vietnamese War.

The primary literature I'll reference is from a Chinese gusano professor, Xiaoming Zhang, who worked for the US Air War College (and ironically was later recently targetted by the FBI China Initiative and subsequently lost his job): "Zhang, X. 2015. Deng Xiaoping's Long War: The Conflict between China and Vietnam, 1979-1991. University of North Carolina Press." As it was sponsored by the literal US DoD (the first book I've ever read where there's a disclaimer that says: "The views expressed in this book are mine and do not necessarily reflect the official policy or position of the U.S. Department of the Air Force, the U.S. Department of Defense, or the U.S. government."), it is obviously ideologically reactionary but because it is meant to provide for the US military an account of PLA strategic planning and thus largely focuses on military analysis, that part is therefore worth reading.

The Sino-Vietnamese War is actually the war in all with the most parallels to the Russo-Ukrainian conflict. Deng's intentions for the war with Vietnam was principally "attitude adjustment." Vietnam had sided with the USSR in the Sino-Soviet Split and this was seen as a betrayal of China's support in the Vietnam War. It started with an initial invasion that was then, by Vietnamese argumentation, repelled. This is what NATOpedia classifies as the "official" Sino-Vietnamese War and in the Vietnamese narrative, it repelled an invader that was planning to sweep their their way through Hanoi all the way down to the Mekong Delta. But then the conflict kept going on.

As the author writes:

The Vietnamese leadership never seemed to comprehend the PRC’s strategy and war objectives, persistently maintaining that the 1979 invasion simply constituted a prelude to Beijing’s long-term scheme of infringing on Vietnamese sovereignty and independence. After China announced its withdrawal on 5 March, Hanoi called for a nationwide general mobilization for the war and began constructing defensive positions in and around Hanoi. By the end of May, the PLA had reverted to its normal alert status. Vietnam, however, remained on guard, stationing a large number of PAVN troops (allegedly 300,000) along border with China at a time when the economy was “in a worse state than at any time since 1975.”

As a result, Hanoi’s attempts to fight simultaneously in Cambodia and on its northern border took a growing national economic and social toll, subsuming Hanoi’s effort to modernize its economy and, more important, undermining its geopolitical ambitions. According to Fred Charles Iklé, “Governments tend to lose sight of the ending of wars and the nation’s interests that lie beyond it,” and many are “blind in failing to perceive that it is the outcome of the war, not the outcome of the campaigns within it” that determines how well their policies serve the nation’s interests. The Vietnamese leadership clearly failed to grasp the gravity of the situation and continued depending on the Soviet Union until its collapse in 1991. If the Vietnamese should draw any lessons from the 1979 war with China, one is, as one Vietnamese general later remarked, “We must learn how to live with our big neighbor.

By the conclusion of the border war in 1991-93, the Socialist Republic of Vietnam, liberated from the US occupation and unified for over 20 years had still been unable to properly focus on its Doi Moi economic reforms, announced in 1986, due to the ongoing conflict:

In the end, only in 1990, after Vietnam’s withdrawal from Cambodia, did the PLA pull its forces back from the occupied Vietnamese hills. Vietnam’s national pride and domestic politics made Hanoi’s leadership unable to tolerate Chinese occupation of any Vietnamese territory, even hills in the remote border region, and it therefore responded to Chinese military pressure with a tit-for-tat strategy. After 1984, Vietnam vigorously resisted Chinese military encroachments, initiating attacks and counterattacks with huge forces even when its economy was weak. Although the fighting took place far from Vietnam’s political and industrial heartland, the conflict encumbered the country’s economy for a long period of time. For China, battlefield costs were fractional at a time of economic prosperity. In this way, China strategically outmaneuvered Vietnam. Since the Hanoi leadership played into Beijing’s hands, China’s military pressure appears to have worked.

In June 1990, during his meeting with the Chinese ambassador in Hanoi, (General Secretary of the CPV) Nguyen Van Linh claimed to have been a student of Mao’s revolutionary theory and stated his great appreciation for China’s aid during Vietnam’s struggles against the French and Americans. He then admitted that Vietnam had wronged China and was willing to correct its mistakes. With respect to Cambodia, the Vietnamese leader expressed confidence that the situation would be resolved peacefully but urged both Vietnam and China to work together to prevent the West and the UN from meddling in Cambodia in the future. The exclusion of the Khmer Rouge from a future Cambodian government, Nguyen Van Linh admitted, was impractical.

The author also makes an allegation of an "agreement" between the two Communist Parties, which is rather interesting in light of the much hyped public Vietnamese antagonism towards China by the West:

A secret deal may have been made regarding how to address the unpleasant thirteen years so that the interlude would not imperil future Sino-Vietnamese relations. The two sides allegedly reached a tacit agreement that prohibited the media from publishing stories and scholars from conducting studies about the border conflict in hopes that the recent hostility would then fade from memory on both sides of the border. Both countries could then concentrate on rejuvenating their relationship. Once again, Vietnam looked to China for direction and guidance, and the relationship was described officially as “good neighbors, good friends, good comrades, good partners” (haolinju, haopengyou, haotongzhi, haohuoban).